Blancpain Fifty Fathoms

The strap size depends on the reference. Yours is engraved on the case back or between the lugs at 6 o'clock.

20 to 23 mm

Verification: Listed by the maker for ref. 5010 12B30 B64B, 5010B 1130 NABA and 1 more

40 to 45 mm cases · 2025

Official page: Blancpain

Indicative information. Check your watch before buying a strap: whatsmylugwidth.com is not responsible for an incorrect size.

Collection104 references

Illustration drawn to scale: 45 mm case, 23 mm lugs

104 Blancpain Fifty Fathoms references

Blancpain Fifty Fathoms references in our database. Each card says where its width comes from: listed by the maker (linked to the maker's page in the details), two independent sources agree, or listed in our database and not yet verified by us.

5008 11B40 NAOA

Fifty Fathoms Fifty

Lug width: 20 mm
Source: Database

Case size: 40.3 mmBlue / Navy dial

Attachment
classic lugs

Status
Listed in our database, not yet verified
5010 12B30 B64B

Fifty Fathoms Fifty

Lug width: 21.5 mm
Source: Maker

Status
Listed by the maker
5010B 1130 NABA

Fifty Fathoms Fifty

Lug width: 21.5 mm
Source: Maker

Status
Listed by the maker
5010C 1130 NABA

Fifty Fathoms Fifty

Lug width: 21.5 mm
Source: Maker

Status
Listed by the maker
5015B‑1130‑52

Fifty Fathoms

Lug width: Screwed bars
Source: Database
50015‑12B34‑52B

Fifty Fathoms 500 Fathoms Cannes 2009

Lug width: Screwed bars
Source: Database
50015A‑12B30‑52B

Fifty Fathoms 500 Fathoms Only Watch 2009

Lug width: Screwed bars
Source: Database
50015‑12B30‑52B

Fifty Fathoms 500 Fathoms Titanium / Black / Black Canvas

Lug width: Screwed bars
Source: Database
5901‑5630‑NANA

Fifty Fathoms 70th Anniversary Act 3 2025

Lug width: 20 mm
Source: Database

Case size: 42 mmYear: 2025Blue dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Display back
Production
2025-present

Status
Listed in our database, not yet verified
5010‑1130‑71S

Fifty Fathoms Automatique 42mm Steel

Lug width: Screwed bars
Source: Database

Case size: 42 mm
5010‑1130‑B64B

Fifty Fathoms Automatique 42mm Steel

Lug width: Screwed bars
Source: Database

Case size: 42 mm
5010‑1130‑NABA

Fifty Fathoms Automatique 42mm Steel

Lug width: Screwed bars
Source: Database

Case size: 42 mm
5015‑1130‑52

Fifty Fathoms Automatique 45 Black

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Sapphire back
Production
2007, present

Status
Listed in our database, not yet verified
5015‑1130‑71

Fifty Fathoms Automatique 45 Blue

Lug width: 23 mm
Source: Database

Case size: 45 mmBlue Sunburst dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Sapphire back
Production
2010, present

Status
Listed in our database, not yet verified
5015‑11C30‑52

Fifty Fathoms Automatique 45 Ceramic Black

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: Ceramic

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Sapphire back
Production
2015, present

Status
Listed in our database, not yet verified
5015‑1130‑71A

Fifty Fathoms Automatique 45 Limited Tribute to 1953

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Sapphire back
Production
2010-2013

Status
Listed in our database, not yet verified
5015‑3630‑52

Fifty Fathoms Automatique 45 Rose Gold

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: Rose Gold

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Sapphire back
Production
2011, present

Status
Listed in our database, not yet verified
5015‑3630‑71B

Fifty Fathoms Automatique 45 Rose Gold Blue

Lug width: 23 mm
Source: Database

Case size: 45 mmBlue dialCase material: Rose Gold

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Sapphire back
Production
2013, present

Status
Listed in our database, not yet verified
5015‑12B30‑52

Fifty Fathoms Automatique 45 Titanium

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: Titanium

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Sapphire back
Production
2019, present

Status
Listed in our database, not yet verified
5015‑12B40‑52

Fifty Fathoms Automatique 45 Titanium Blue

Lug width: 23 mm
Source: Database

Case size: 45 mmBlue dialCase material: Titanium

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Sapphire back
Production
2020, present

Status
Listed in our database, not yet verified
5015‑1130‑52A

Fifty Fathoms Automatique Black

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Screw steel
Production
2007, present

Status
Listed in our database, not yet verified
5015‑1130‑71B

Fifty Fathoms Automatique Blue

Lug width: 23 mm
Source: Database

Case size: 45 mmBlue dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Screw steel
Production
2010, present

Status
Listed in our database, not yet verified
5015‑11C30‑52A

Fifty Fathoms Automatique DLC / Black / Black Canvas

Lug width: Screwed bars
Source: Database
5050‑12B30‑B52A

Fifty Fathoms Automatique Grande Date

Lug width: 23 mm
Source: Database

Case size: 45 mmBlue dialCase material: Titanium

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Screw titanium
Production
2019, present

Status
Listed in our database, not yet verified
5050‑12B30‑NABA

Fifty Fathoms Automatique Grande Date Titanium / Black / Black NATO

Lug width: 23 mm
Source: Database
5015A‑3630‑63B

Fifty Fathoms Automatique Red Gold / Black / Brown Barenia

Lug width: Screwed bars
Source: Database
5015‑3603C‑63B

Fifty Fathoms Automatique Red Gold / Blue / Calf

Lug width: Screwed bars
Source: Database
5015‑3630‑52A

Fifty Fathoms Automatique Rose Gold

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: Yellow Gold

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Screw gold
Production
2015, present

Status
Listed in our database, not yet verified
5015D‑1140‑52B

Fifty Fathoms Automatique Stainless Steel / Blue / Blue Canvas

Lug width: Screwed bars
Source: Database
5015D‑1140‑71B

Fifty Fathoms Automatique Stainless Steel / Blue / Bracelet

Lug width: Screwed bars
Source: Database
5015‑1144‑52

Fifty Fathoms Automatique Stainless Steel / Mother of Pearl / White Canvas

Lug width: Screwed bars
Source: Database
5015‑1127‑52A

Fifty Fathoms Automatique Stainless Steel / White / White Canvas

Lug width: Screwed bars
Source: Database
5015A‑1144‑52A

Fifty Fathoms Automatique Stainless Steel / White Mother Of Pearl / White Canvas

Lug width: Screwed bars
Source: Database
5010‑1130‑B52B

Fifty Fathoms Automatique Steel 42.3mm - Black on Sail-Canvas Strap

Lug width: 21.5 mm
Source: Database

Case size: 42.3 mm
5010‑1130‑B52A

Fifty Fathoms Automatique Steel 42.3mm - Black on Sail-Canvas Strap

Lug width: 21.5 mm
Source: Database

Case size: 42.3 mm
5010‑1130‑B64A

Fifty Fathoms Automatique Steel 42mm - Black on Rubber Strap

Lug width: 21.5 mm
Source: Database

Case size: 42 mm
5015‑1130‑71S

Fifty Fathoms Automatique Steel 45mm - Black on Bracelet

Lug width: 23 mm
Source: Database

Case size: 45 mm
5015‑12B30‑B52A

Fifty Fathoms Automatique Titanium

Lug width: 23 mm
Source: Database

Case size: 45 mmGrey dialCase material: Titanium

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Screw titanium
Production
2018, present

Status
Listed in our database, not yet verified
5015‑12B30‑98B

Fifty Fathoms Automatique Titanium / Black / Bracelet

Lug width: Screwed bars
Source: Database
5015‑12B30‑NABA

Fifty Fathoms Automatique Titanium / Black / NATO

Lug width: Screwed bars
Source: Database
5015‑12B30‑B52B

Fifty Fathoms Automatique Titanium / Black / Sailcloth

Lug width: Screwed bars
Source: Database
5010‑12B30‑98S

Fifty Fathoms Automatique Titanium 42.3mm - Black on Bracelet

Lug width: 21.5 mm
Source: Database

Case size: 42.3 mm
5010‑12B30‑B52A

Fifty Fathoms Automatique Titanium 42.3mm - Black on Sail-canvas Strap

Lug width: 21.5 mm
Source: Database

Case size: 42.3 mm
5010‑12B30‑B64A

Fifty Fathoms Automatique Titanium 42.3mm - Black on Tropic Rubber Str

Lug width: 21.5 mm
Source: Database

Case size: 42.3 mm
5010‑12B40‑98S

Fifty Fathoms Automatique Titanium 42.3mm - Blue on Bracelet

Lug width: 21.5 mm
Source: Database

Case size: 42.3 mm
5010‑12B40‑O52A

Fifty Fathoms Automatique Titanium 42.3mm - Blue on Sail-canvas Strap

Lug width: 21.5 mm
Source: Database

Case size: 42.3 mm
5008B‑1130‑B52A

Fifty Fathoms Barakuda

Lug width: 20 mm
Source: Database

Case size: 40 mmBlack/Red dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Sapphire back
Production
2019-2019

Status
Listed in our database, not yet verified
5008B‑1130‑B64A‑TROP

Fifty Fathoms Barakuda Tropical

Lug width: 20 mm
Source: Database

Case size: 40 mmBrown Tropical dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Screw steel
Production
2020, present

Status
Listed in our database, not yet verified
5052‑1110‑063A

Fifty Fathoms Bathygraphe Jour Date 70s Stainless Steel / Brown / Dark brown Calf

Lug width: 23 mm
Source: Database

Case size: 43 mmBlack dialCase material: Stainless Steel
5071‑1110‑B52A

Fifty Fathoms Bathygraphe Quantieme Annuel Grey / Black Canvas

Lug width: 23 mm
Source: Database

Case size: 43 mmGrey dialCase material: Stainless Steel
5071‑1110‑NABA

Fifty Fathoms Bathygraphe Quantieme Annuel Grey / Black NATO

Lug width: 23 mm
Source: Database

Case size: 43 mmGrey dialCase material: Stainless Steel
5071‑1110‑70B

Fifty Fathoms Bathygraphe Quantieme Annuel Grey / Steel Bracelet

Lug width: 23 mm
Source: Database

Case size: 43 mmGrey dialCase material: Stainless Steel
5054‑1110‑NABA

Fifty Fathoms Bathygraphe Quantieme Complet Grey / Black NATO

Lug width: 23 mm
Source: Database
5054‑1110‑70B

Fifty Fathoms Bathygraphe Quantieme Complet Grey / Stainless Steel bracelet

Lug width: 23 mm
Source: Database

Case size: 43 mmGrey dialCase material: Stainless Steel
5054‑1210‑G52A

Fifty Fathoms Bathygraphe Quantieme Complet Titanium / Grey / Canvas

Lug width: 23 mm
Source: Database
5054‑1210‑NAGA

Fifty Fathoms Bathygraphe Quantieme Complet Titanium / Grey / NATO

Lug width: 23 mm
Source: Database
5000‑0130‑NABA

Fifty Fathoms Bathyscaphe Ceramic / Black / NATO

Lug width: 23 mm
Source: Database

Case size: 43.6 mmBlack dialCase material: Ceramic
5200‑0130‑B52A

Fifty Fathoms Bathyscaphe Flyback Chronograph Black Ceramic / Black / Black Canvas

Lug width: 23 mm
Source: Database

Case size: 43.6 mmBlack dialCase material: Ceramic
5200‑0130‑NABA

Fifty Fathoms Bathyscaphe Flyback Chronograph Black Ceramic / Black / Black Nato

Lug width: 23 mm
Source: Database

Case size: 43.6 mmBlack dialCase material: Ceramic
5200‑1110‑NABA

Fifty Fathoms Bathyscaphe Flyback Chronograph Stainless Steel / Grey / Black Nato

Lug width: 23 mm
Source: Database
5200‑1110‑70B

Fifty Fathoms Bathyscaphe Flyback Chronograph Stainless Steel / Grey / Bracelet

Lug width: 23 mm
Source: Database

Case size: 43 mmGrey dialCase material: Stainless Steel
5200‑0310‑G52A

Fifty Fathoms Bathyscaphe Ocean Commitment II Flyback Chronograph

Lug width: 23 mm
Source: Database
5000‑36S30‑B52A

Fifty Fathoms Bathyscaphe Sedna Gold / Black / Black Canvas

Lug width: 23 mm
Source: Database

Case size: 43 mmBlack dialCase material: Sedna Gold
5000‑36S30‑NABA

Fifty Fathoms Bathyscaphe Sedna Gold / Black / Grey Nato

Lug width: 23 mm
Source: Database

Case size: 43 mmBlack dialCase material: Sedna Gold
5000‑1110‑NABA

Fifty Fathoms Bathyscaphe Stainless Steel / Grey / Grey Nato

Lug width: 23 mm
Source: Database

Case size: 43 mmGrey dialCase material: Stainless Steel
5000‑1110‑K52A

Fifty Fathoms Bathyscaphe Stainless Steel / Grey / Sand Canvas

Lug width: 23 mm
Source: Database

Case size: 43 mmGrey dialCase material: Stainless Steel
5000‑1110‑NAKA

Fifty Fathoms Bathyscaphe Stainless Steel / Grey / Sand Nato

Lug width: 23 mm
Source: Database

Case size: 43 mmGrey dialCase material: Stainless Steel
5000‑1230‑B52A

Fifty Fathoms Bathyscaphe Titanium / Black / Black Canvas

Lug width: 23 mm
Source: Database

Case size: 43 mmBlack dialCase material: Titanium
5000‑1230‑NABA

Fifty Fathoms Bathyscaphe Titanium / Black / Grey Nato

Lug width: 23 mm
Source: Database

Case size: 43 mmBlack dialCase material: Titanium
5000‑1230‑K52A

Fifty Fathoms Bathyscaphe Titanium / Black / Sand Canvas

Lug width: 23 mm
Source: Database

Case size: 43 mmBlack dialCase material: Titanium
5000‑1230‑NAKA

Fifty Fathoms Bathyscaphe Titanium / Black / Sand Nato

Lug width: 23 mm
Source: Database

Case size: 43 mmBlack dialCase material: Titanium
5010‑12B40‑O64B

Fifty Fathoms Brushed Titanium 42.3mm - Blue on Rubber Strap

Lug width: 21.5 mm
Source: Database

Case size: 42.3 mm
5085F‑1130‑52A

Fifty Fathoms Chronograph Flyback Black

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic Chronograph
Caseback
Screw steel
Production
2008, present

Status
Listed in our database, not yet verified
5085F‑1130‑71B

Fifty Fathoms Chronograph Flyback Blue

Lug width: 23 mm
Source: Database

Case size: 45 mmBlue dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic Chronograph
Caseback
Screw steel
Production
2012, present

Status
Listed in our database, not yet verified
5085F‑3630‑52A

Fifty Fathoms Chronograph Rose Gold

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: Yellow Gold

Attachment
classic lugs
Style
diver
Movement
Automatic Chronograph
Caseback
Screw gold
Production
2014, present

Status
Listed in our database, not yet verified
5085F‑1130‑71

Fifty Fathoms Chronographe Flyback Blue

Lug width: 23 mm
Source: Database

Case size: 45 mmBlue dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic flyback
Caseback
Sapphire back
Production
2010, present

Status
Listed in our database, not yet verified
5085F‑3630‑52

Fifty Fathoms Chronographe Flyback Red Gold / Black / Black Canvas

Lug width: Proprietary strap system
Source: Database
5085FA‑3630‑63B

Fifty Fathoms Chronographe Flyback Rose Gold

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: Rose Gold

Attachment
classic lugs
Style
diver
Movement
Automatic flyback
Caseback
Sapphire back
Production
2011, present

Status
Listed in our database, not yet verified
5085F.B‑1140‑52B

Fifty Fathoms Chronographe Flyback Stainless / Blue / Blue Canvas

Lug width: Proprietary strap system
Source: Database
5085F.B‑1140‑71B

Fifty Fathoms Chronographe Flyback Stainless Steel / Blue / Bracelet

Lug width: Proprietary strap system
Source: Database
5085F‑1130‑52

Fifty Fathoms Chronographe Flyback Steel

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic flyback
Caseback
Sapphire back
Production
2007, present

Status
Listed in our database, not yet verified
5785F‑11D03‑63A

Fifty Fathoms Flyback Chronograph Speed Command Orange

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: Stainless Steel
5785F.B‑11D03‑63A

Fifty Fathoms Flyback Chronograph Speed Command Red

Lug width: 23 mm
Source: Database

Case size: 45 mmGrey dialCase material: Stainless Steel
5785F.A‑11D03‑63A

Fifty Fathoms Flyback Chronograph Speed Command Yellow

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: Stainless Steel
50021‑12B30‑52B

Fifty Fathoms GMT / Black / Canvas

Lug width: Screwed bars
Source: Database
5066F‑1140‑52B

Fifty Fathoms GMT Steel

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack Gmt dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic GMT
Caseback
Screw steel
Production
2011, present

Status
Listed in our database, not yet verified
5050‑12B30‑98B

Fifty Fathoms Grande Date Titanium

Lug width: 23 mm
Source: Database

Case size: 45 mmBlue dialCase material: Titanium

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Screw titanium
Production
2019, present

Status
Listed in our database, not yet verified
5008‑1130‑NAVA

Fifty Fathoms Hodinkee LE

Lug width: 20 mm
Source: Database

Case size: 40 mmBlue Matte dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Screw steel
Production
2018-2019

Status
Listed in our database, not yet verified
5008‑1130‑B52A

Fifty Fathoms MIL-SPEC Limited

Lug width: 20 mm
Source: Database

Case size: 40 mmBlack Moisture Dot dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Sapphire back
Production
2017-2017

Status
Listed in our database, not yet verified
5008‑1130‑71S

Fifty Fathoms MIL-SPEC Stainless Steel / Black / Bracelet

Lug width: 20 mm
Source: Database

Case size: 40.3 mmBlack dialCase material: Stainless Steel

Attachment
classic lugs

Status
Listed in our database, not yet verified
5015E‑1130‑B52A

Fifty Fathoms Nageurs de Combat

Lug width: Screwed bars
Source: Database
5008D‑1130‑B64A

Fifty Fathoms No Rad Limited

Lug width: 20 mm
Source: Database

Case size: 40 mmBlack dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Sapphire back
Production
2021-2021

Status
Listed in our database, not yet verified
5015‑12B40‑NAOA

Fifty Fathoms Stainless Steel / Blue / Blue NATO

Lug width: Screwed bars
Source: Database
5015‑12B40‑98

Fifty Fathoms Titanium / Blue / Bracelet

Lug width: Screwed bars
Source: Database
5015‑12B40‑O52A

Fifty Fathoms Titanium No-Date

Lug width: 23 mm
Source: Database

Case size: 45 mmGrey dialCase material: Titanium

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Screw titanium
Production
2020, present

Status
Listed in our database, not yet verified
5025‑1530‑52A

Fifty Fathoms Tourbillon

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: White Gold
5025‑36B40‑O52B

Fifty Fathoms Tourbillon 8 Days Red Gold 45mm - Blue on Fabric Strap

Lug width: 23 mm
Source: Database

Case size: 45 mm

Attachment
classic lugs

Status
Listed in our database, not yet verified
5025‑3630‑52A

Fifty Fathoms Tourbillon 8 Jours Red Gold / Black / Black Canvas

Lug width: 23 mm
Source: Database
5025‑9530‑52A

Fifty Fathoms Tourbillon 8 Jours Red Gold / Diamonds / Black Canvas

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: Red Gold
5025‑6230‑52A

Fifty Fathoms Tourbillon 8 Jours Red Gold / Diamonds / Black Canvas

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: Red Gold
5025‑9430‑52A

Fifty Fathoms Tourbillon 8 Jours White Gold / Diamonds / Black Canvas

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: White Gold
5025‑5230‑52A

Fifty Fathoms Tourbillon 8 Jours White Gold / Diamonds / Black Canvas

Lug width: 23 mm
Source: Database

Case size: 45 mmBlack dialCase material: White Gold
5015C‑1130‑52B

Fifty Fathoms Tribute to Fifty Fathoms Aqua Lung

Lug width: Screwed bars
Source: Database
5008‑11B40‑52A

Fifty Fathoms X Ocean Commitment III

Lug width: 20 mm
Source: Database

Case size: 40 mmBlue dialCase material: Steel

Attachment
classic lugs
Style
diver
Movement
Automatic
Caseback
Sapphire back
Production
2018-2018

Status
Listed in our database, not yet verified

FAQ

What lug width does the Blancpain Fifty Fathoms use?

Blancpain Fifty Fathoms lug width: 20 to 23 mm depending on the reference. The most common is 23 mm (57 of the 78 references with a listed width in our database). Find your exact reference in the table below. The Blancpain Fifty Fathoms ref. 5010 12B30 B64B, 5010B 1130 NABA and 1 more take 21.5 mm (listed by the maker).

Do all Blancpain Fifty Fathoms references take the same strap?

No. 3 different lug widths appear across the line, often by case size or generation. Check the reference engraved on the case back or between the lugs.

Where do these Blancpain Fifty Fathoms lug widths come from?

From our database, which lists 104 Blancpain Fifty Fathoms references, 78 of them with a listed width. Each reference card says whether the maker lists the width, two independent sources agree on it, or it is not yet verified.

Other Blancpain collections

All Blancpain collections

Help

What is lug width?

The gap between the two lugs that hold the strap, in millimetres. A new strap must match it exactly: 20 mm lugs take a 20 mm strap.

Measure it in 30 seconds

Take the strap off, or look at the back of it: many straps print their width.
Measure the inside gap between the lugs with a caliper or a millimetre ruler.
Round to the nearest whole millimetre. Most watches use 18, 20 or 22 mm.

Strap, quick release or system?

Most watches use spring bars, so any strap of the right width fits. Many smartwatches use their own band system instead, such as Apple Watch bands or Garmin QuickFit.