What size band does a Seiko 5 take?

It depends which Seiko 5. The small SNK models (SNK809 and siblings) take 18mm straps. The Seiko 5 Sports SRPD line in its standard 42.5mm case takes 22mm, and the Seiko 5 Sports GMT SSK models also take 22mm. Check the reference on the caseback against the table, because Seiko spreads the 5 family across 18, 20 and 22mm.

Will a 22mm strap fit my Seiko diver?

Most Seiko divers take a 22mm strap at the lugs: SKX007, SKX009, Turtle SRP777, Samurai, and the Tuna family. The exceptions are the mid-size SKX013 at 20mm and the 20mm group of larger divers (Sumo, Monster, MM300, MM200, 62MAS reissue). Width is only half the story on a Seiko diver: most use 2.5mm thick fat spring bars, so a standard 1.8mm bar will feel loose.

What strap size is a Grand Seiko?

Grand Seiko uses three widths across the range and case size does not predict them. The SBGA211 Snowflake and the SLGH005 White Birch differ by a millimeter (20mm versus 22mm) despite both being 40 to 41mm watches. The SBGW231 dress watch uses 19mm, and the titanium Heritage Four Seasons references such as the SBGA413 Shunbun use 21mm. Always check the specific reference.

Seiko Watch Band Size by Model

Seiko is the most strap-swapped brand in watch collecting, and also the brand where the sizing questions pile up: the 5 family alone spans three widths, the divers split into a 20mm camp and a 22mm camp, and Grand Seiko hides odd 19 and 21mm widths in its dressier references. This page lists the strap width, the width between the lugs, for the mainstream Seiko and Grand Seiko models people actually buy straps for. Every row is confirmed by two independent sources, and the one cell where the sources disagree is flagged rather than averaged.

The one-line answer: small Seiko 5 SNK models take 18mm, Seiko 5 Sports SRPD and the SKX007/Turtle/Samurai divers take 22mm, the Sumo/Monster/MM300 divers take 20mm, the Alpinist takes 20mm, Presage takes 20mm, and Grand Seiko runs 19, 20, 21 and 22mm depending on the reference. And on most Seiko divers the spring bars themselves are fat 2.5mm bars, a separate trap covered below.

Seiko strap width by collection and model

Model	Case	Band width	Notes
Seiko 5 SNK809 / SNK807 / SNK805	37-38mm	18mm	The small 5; the classic budget 18mm strap platform
Seiko 5 Sports SRPD (SRPD55 and siblings)	42.5mm	22mm	The SKX successor; fat 2.5mm spring bars
Seiko 5 Sports GMT SSK	42.5mm	22mm	Same 22mm family as the SRPD line
Presage Cocktail Time (SARB065, SRPB41, SSA lines)	40-40.5mm	20mm	Dress line; consistent 20mm across references
Presage SARY055 and Sharp Facet series	41mm	22mm	The larger Presage case steps up to 22mm
Prospex Turtle (SRP777, SRPB11, SRPE family)	44-45mm	22mm	Fat bars; the 42mm Mini Turtle is 20mm
Prospex Samurai (SRPB09, SRPD23 and siblings)	43.8-44mm	22mm	One early 20mm listing (SRPC07) flagged below
Prospex Tuna (SBBN013, SBBN039, SRPA81, SBDX011)	47-52mm	22mm	Shrouded divers; fixed-width 22mm throughout
SKX007 / SKX009 (discontinued)	42.5mm	22mm	The reference 22mm diver; fat 2.5mm bars
SKX013 mid-size (discontinued)	37-38mm	20mm	Not interchangeable with the SKX007's 22mm
Alpinist SARB017 (discontinued)	38-39mm	20mm	Current SPB121 reissue is also 20mm
Alpinist SPB121	39.5mm	20mm	All current Alpinist references are 20mm
Sumo (SBDC001, SPB143 62MAS style)	40.5-45mm	20mm	Big case, 20mm lugs; a wide-taper bracelet
Monster (SRP307, SRPD27 and earlier generations)	42-42.4mm	20mm	Not 22mm despite the aggressive case
Marine Master 300 (SBDX017, SPB255 style)	44mm	20mm	MM200 also 20mm
62MAS reissue SLA017 (discontinued)	40mm	19mm	The odd-width vintage tribute
SARB033 / SARB035 (discontinued)	38mm	20mm	The classic 38mm dress-sport pair

One disagreement worth flagging: the entry-level Samurai SRPC07 is listed at 20mm by StrapsCo and 22mm by the Strapcode dimension table. Everything around it in both sources says the Samurai line is 22mm, so treat 20mm for that one discontinued reference as unconfirmed and measure before ordering an odd-width strap. Every other row above matched across at least two independent sources.

The fat spring bar warning, before you order anything

On Seiko divers the band width is only half the fit question. The SKX007, Turtle, and most Prospex divers use oversized 2.5mm thick spring bars with 1.1mm tips (Seiko part C220FS) instead of the standard 1.8mm bar. A standard bar will fit the strap but sit loose in the lug holes. This is a spring bar question rather than a width question, so the full part numbers, sizes, and ordering cautions live on the spring bar sizes page, and the tool for swapping them on the spring bar tool page.

Grand Seiko strap widths, reference by reference

Grand Seiko deserves its own table because case diameter does not predict lug width here, and because one widely-read dimension site gets the Snowflake wrong. Current Grand Seiko bracelets and straps are 19, 20, 21 or 22mm wide at the lugs:

Model	Case	Band width	Notes
SBGA211 "Snowflake" (Spring Drive titanium)	41mm	20mm	Official Grand Seiko spec; one aggregator's 21mm is wrong (flagged below)
SLGH005 "White Birch" (Hi-Beat)	40mm	22mm	Official spec; bracelet tapers 22 to 20mm
SBGA413 "Shunbun" ( titanium Heritage Four Seasons)	40mm	21mm	The odd size most retailers stock poorly
SBGW231 (Elegance manual-wind)	37.3mm	19mm	Slim dress reference; 19mm like a vintage Submariner
Sport divers 200m (SBGA463 style, 44.2mm)	44.2mm	20mm	Spring Drive and Hi-Beat sport models

The flagged cell: WristBuzz's otherwise useful Grand Seiko dimension table lists the Snowflake at 21mm, but Grand Seiko's own SBGA211 specification page says band width 20mm, StrapsCo's Snowflake fitment page says 20mm, and the aftermarket consensus (CNS Watch Bands' Grand Seiko guide) is 20mm. Buy 20mm. The same aggregator's 20mm figure for the White Birch SLGH005 is also wrong; the official page says 22mm, matched by dealer listings. When two sources disagree on a Grand Seiko width, the official specification page wins.

Interchange families, so you can reuse straps

The 22mm family: Seiko 5 Sports SRPD and SSK GMT, SKX007/SK009, Turtle, Samurai, Tuna, Presage SARY. One 22mm strap rotation serves almost the whole modern sport line, with the fat-bar caveat on divers.
The 20mm family: Alpinist old and new, Presage Cocktail Time, Sumo, Monster, MM300, MM200, SKX013, SARB033/035. Also the width shared with Hamilton Khaki Field and most Samsung Galaxy Watches.
The odd ones: SNK's 18mm, the SLA017's 19mm, and Grand Seiko's 19/21mm references. Aftermarket selection thins out sharply at odd widths, which is worth knowing before you fall in love with a strap that only comes in even sizes.

Finding your own number if the table misses it

Seiko's reference number is on the caseback, and the movement number beside it, which is how the fitment pages cited below are indexed. If your reference is not in the table, measure the gap between the lugs where the strap sits: the measuring guide covers the technique, the lug width chart explains what the number means for strap shopping, and the watch database carries case dimensions for popular Seikos if you also want diameter and lug-to-lug. For whether a 44mm Turtle or 45mm Sumo suits your wrist at all, that is the case size by wrist question, separate from band width.

Related guides

Once you know the width: watch band materials compared for what to buy, strap length by wrist so the new strap is also long enough, and how to adjust a watch band when the fit is close but not right. The sibling brand pages are the Casio strap size chart and the Citizen band size chart; Casio's digitals share Seiko's 18mm but its G-Shocks do not take standard straps at all. The Timex band size chart covers the brand where nearly everything is 20mm, and the watch strap taper chart explains the second number in a 20/16 listing.

Sources

Seiko 5 SNK809 18mm: Strapcode's Seiko dimension table (18mm, 38mm case), corroborated by StrapsCo's SNK fitment listings and Lug and Leather's model chart.
Seiko 5 Sports SRPD 22mm: Strapcode's dimension table, corroborated by Lug and Leather's chart (SRPD/SKX-successor 22mm) and StrapsCo's SRPD-family fitment pages.
SSK GMT 22mm: Lug and Leather's Seiko table, corroborated by StrapsCo's Seiko 5 Sports fitment listings.
Presage Cocktail Time 20mm (SARB065, SRPB41, SSA): StrapsCo's Presage fitment table (20mm across Cocktail references), corroborated by Strapcode's Cocktail Time Power Reserve row.
Presage SARY055 22mm: StrapsCo's SARY055 fitment row, corroborated by its Presage family table consistency (41mm case, 22mm).
Turtle SRP777/SRPB11/SRPE 22mm: Strapcode's SRP777 row, corroborated by StrapsCo's Turtle fitment rows and Lug and Leather's chart.
Samurai 22mm: Strapcode's Samurai row and StrapsCo's SRPB09/SRPD23 rows; the SRPC07 20mm disagreement between the two is flagged in the text.
Tuna 22mm: Strapcode's Tuna rows (SBBN013, SBBN039, SBDX016, SRPA82), corroborated by StrapsCo's Tuna fitment rows (SBBN015, SBDX011, SRPA81).
SKX007 22mm: StrapsCo's SKX007/SK009 fitment pages, corroborated by Strapcode's dimension table and Delugs' SKX007 strap guide.
SKX013 20mm: StrapsCo's SKX013 fitment page, corroborated by Hodinkee's SKX013 Value Proposition review (20mm lug width).
Alpinist SARB017 20mm: StrapsCo's Alpinist row, corroborated by Strapcode's Alpinist row (20mm).
Alpinist SPB121 20mm: Delugs' Alpinist strap page, corroborated by CNS Watch Bands' Alpinist guide and Hemsut's Alpinist band list.
Sumo 20mm (SBDC001, SPB143): Strapcode's Sumo row, corroborated by StrapsCo's SBDC001 row; SPB143 20mm per Delugs' SPB143 guide and StrapHabit's 62MAS sizing page.
Monster 20mm: Strapcode's Monster row (20mm), corroborated by CNS Watch Bands' Monster guide (42mm SRPD/SRPE/SRP3xx generation all 20mm) and StrapsCo's SRPD27/SRP313/SRP315 rows.
MM300 20mm: Strapcode's MM300 row, corroborated by StrapsCo's SBDX017 row (20mm).
SLA017 19mm: StrapsCo's SLA017 fitment row, corroborated by Strapcode's SLA017 row (19mm).
SARB033 20mm: Strapcode's row, corroborated by StrapsCo's SARB033 row.
Grand Seiko SBGA211 20mm: Grand Seiko's official SBGA211 specification page (band width 20mm), corroborated by StrapsCo's Snowflake fitment page and CNS Watch Bands' Grand Seiko guide; WristBuzz's 21mm flagged in the text.
Grand Seiko SLGH005 22mm: Grand Seiko's official SLGH005 specification page (band width 22mm), corroborated by Skeies dealer listing and Majestix Collection's comparison (22mm tapering to 20mm); WristBuzz's 20mm flagged in the text.
Grand Seiko SBGA413 21mm: Grand Seiko's official SBGA413 specification page (band width 21mm), corroborated by CNS Watch Bands' Grand Seiko guide.
Grand Seiko SBGW231 19mm: CNS Watch Bands' Grand Seiko guide and dealer specs from Timepiece, Bandiera Jewellers, and Shopping in Japan (19mm band width, 37.3mm case).
Grand Seiko sport divers 20mm: WristBuzz's dimension table (SBGA463, SBGH257), corroborated by Grand Seiko's published sport-collection strap widths.
Fat spring bars 2.5mm, part C220FS: Long Island Watch, CPSA Thailand genuine Seiko parts listings, and Masar Shop's compatibility table; details on the spring bar sizes page.