WHOOP Band Size Chart for 4.0, 5.0 and MG

WHOOP is the one mainstream tracker that is sized nothing like a watch. There are no lugs and no spring bars: the sensor slides into a fabric or silicone band on a Fast Link slider, the band wraps around your wrist and hooks onto the sensor, and sizing is done by adjustability, not by picking a strap width. That has two consequences. First, the wrist bands are one-size-fits-all with an adjustable strap, not S/M or L/XL; the only WHOOP bands that come in two sizes are the bicep bands. Second, the generation matters more than the size: 4.0 bands do not fit 5.0 or MG hardware, and 5.0 bands are not meant for MG. This chart separates all three questions, generation, wrist fit and bicep sizing, with WHOOP's own numbers.

WHOOP band size chart: wrist and bicep bands by generation

Sizing figures are WHOOP's own, from the shop sizing guides and support articles cited per row. Wrist bands adjust continuously rather than coming in lengths, so the wrist rows list the published maximum length instead of a range; your wrist circumference just needs to be under it, and the knit bands cinch down small. Sources are in the Sources section.

*MG note: 5.0 bands physically attach to an MG sensor but are not designed for it; see the compatibility section below. Honest gaps: WHOOP's current US shop renders its sizing accordion behind a login and scripts, so the 5.0/MG wrist-band rows above lean on WHOOP's own whoop.in storefront, which publishes the identical guide text; the LeatherLuxe S/M and L/XL wrist ranges are not printed anywhere first-party at build time, so the row states what is verified (two sizes exist) and nothing more; and WHOOP publishes no official minimum wrist circumference for the knit wrist bands, only the maximum length, so a very small wrist can only be judged by the finger rule below, not by a chart. The 4.0 bicep figures are archived first-party values (2020-era shop page) and are superseded by the current 10-13 / 13-16 in chart for 5.0/MG hardware.

WHOOP does not use lug widths, and the one number that matters

Search for a WHOOP band width in millimeters and you will mostly find third-party sellers quoting their own straps. WHOOP's own sizing guides never frame the wrist bands by width: the bands are one size, and the guide line reads, for SuperKnit, SportFlex and CoreKnit alike, that the band is a one-size-fits-all design with an adjustable strap that shortens or lengthens, reaching a maximum length of 9.5 in (24 cm) with a width of 24mm ^{[2] [3]}. That 24mm figure is close to a watch's lug width, which is why confusion survives, but it is not a compatibility number: you cannot buy a 24mm watch strap and put it on a WHOOP. The only purchase decision on the wrist is the generation, and the only fit decision is how the adjustable strap sits on your wrist, which the finger rule below settles in seconds. The 4.0 generation used the same one-size logic; WHOOP's 4.0-era sizing guide for SuperKnit states it verbatim: SuperKnit bands are all one size, length 9.5 in / 24 cm ^[1].

Bicep band sizing: the only WHOOP bands with real size steps

The bicep band moves the sensor to your upper arm, and because an arm does not take an adjustable wrap the way a wrist does, these bands come in two sizes. For the current 5.0/MG CoreKnit Bicep Band, WHOOP's chart is explicit: S/M fits bicep circumferences between 10 and 13 in, L/XL fits 13 to 16 in, with the metric table printing 25-28 cm and 28-41.5 cm, measured around the fullest part of the bicep with the arm relaxed at your side ^[4]. The 4.0-era chart was different and this is the trap for anyone reading an old guide: the archived official sizing page lists S/M at 12 in / 30.5 cm and L/XL at 17 in / 43.2 cm ^[5]. The old L/XL maxes at 43.2 cm while the new one stretches to 41.5 cm, and the size names are identical, so check which generation a bicep band is for before trusting a range you remember. If you sit between sizes, take the larger one: the bands cinch down, but a small size cannot stretch up, and WHOOP's own fit instruction for the bicep band is that it stay secure without restricting movement or circulation ^[13].

4.0 versus 5.0 versus MG compatibility: what swaps and what does not

This is where WHOOP band buying goes wrong, because the bands look similar across generations and none of them interchange. WHOOP's support center states it directly: WHOOP 4.0 and WHOOP 5.0/MG bands are not cross-compatible, and each generation has its own Fast Link slider design that ensures a secure fit ^[14]. A WHOOP Team answer on the official forum adds the rest of the 4.0 inventory: body items and battery packs from 4.0 are no longer compatible with 5.0, due to the updated hardware and new shape ^[8]. The launch coverage adds the reason: the new generation is 7% smaller and rebuilt around a new charging platform, so 4.0 chargers and bands simply will not fit ^[10]. The matrix:

The MG wrinkle is worth one more line: a 5.0 band will physically attach to an MG device, but MG-specific bands carry a scalloped clasp with conductive coating that the ECG feature needs, so a plain 5.0 band on an MG disables ECG while strain, sleep and recovery still track normally. WHOOP's own community team says exactly this ^[11], and the launch coverage confirms the ECG hardware lives in the redesigned clasp ^[10]. On chargers, only the 4.0 battery pack is stranded on its own generation; the Wireless PowerPack belongs to the 5.0/MG era ^{[8] [10]}.

The sensor itself: 5.0 and MG dimensions

If you are coming from watches and want to know how big the thing on your wrist is, WHOOP prints it: the 5.0 sensor measures 34.7 mm long, 24 mm wide and 10.6 mm high and weighs about 26.5 grams, figures from WHOOP's own support article as quoted in launch coverage ^{[12] [15]}. The 5.0 and MG are both about 7% smaller than the 4.0, which is part of why the band mounts had to change ^[10]. There is no case-size-by-wrist decision to make here the way there is with a round watch; the equivalent decision is wrist versus bicep versus WHOOP Body apparel. One verified wrinkle if you wear the bicep band on MG hardware: WHOOP notes the CoreKnit bicep band is not ECG capable, and Life members with MG devices only get ECG readings while wearing the device on the wrist ^[4].

The finger rule: how a WHOOP band should actually fit

Because the wrist bands are one-size and adjustable, fit is a tension check, not a chart lookup. WHOOP's own accessory setup instructions give the test: the band should feel snug but not too tight, and for best accuracy, if you can fit a finger underneath, it is too loose ^[13]. Placement matters as much as tension: WHOOP's Fast Link guide says to ensure a snug but comfortable fit resting about 1 inch away from the wrist bone ^[14], and the sensor must stay in constant contact with the skin, because a loose band lets light leak under the optical sensor and corrupts heart-rate readings. That is the whole sizing interaction: slide the sensor into the Fast Link slider, secure the clasp into the holes on the other side, pull the loose end to adjust, and snap the clasp closed with the logo facing you ^[13]. For the bicep band the instruction is the upper-arm equivalent: snug, secure, and not restricting movement or circulation ^[13].

How to measure and pick a WHOOP band in three steps

First, identify your sensor generation before anything else, because it gates every accessory: the 4.0 is the thicker pre-2025 sensor, the 5.0 and MG are the 7% smaller 2025 bodies, and the MG is the one with the scalloped ECG clasp. Second, for wrist wear you do not need to measure at all unless your wrist is unusually large: the one-size band adjusts up to 9.5 in / 24 cm around, so any wrist under that circumference with room to spare takes the standard band, and the wrist measuring guide plus the no-tape string method cover getting the number if you want it. Third, for bicep wear measure the fullest part of your upper arm with the muscle relaxed, then take the 5.0/MG chart: 10-13 in means S/M, 13-16 in means L/XL, and exactly 13 in is the boundary where sizing up is the safer call ^[4]. If a wrist band passes the finger rule but irritates, the material is the variable to change, not the size; the fit question for regular watches is covered separately in how should a watch fit.

Related guides

WHOOP is the outlier in this family: every other smartwatch line below is sized by strap width or official wrist ranges, which is the classic watch system. See the smartwatch sizing guide for how sensor bands differ from watch straps, the watch band size chart for the width system itself, and the per-brand pages: Apple Watch (the S/M and L/XL wrist-range method, closest to WHOOP's bicep logic), Galaxy Watch, Fitbit, Garmin, Huawei (the only maker publishing wrist ranges as systematically as WHOOP), Amazfit, COROS, Suunto and Xiaomi. Whether a given case size suits your wrist at all is a separate question in case size by wrist.

Sources

1. WHOOP 4.0 SuperKnit sizing guide, archived first-party shop page data (2021): "SuperKnit bands are all one size. The length of the band is 9.5 in/24 cm." shop.whoop.com via Wayback Machine
2. WHOOP 5.0 SuperKnit product page, WHOOP's official India storefront: "one-size-fits-all design ... maximum length of 9.5 in (24 cm) and has a width of 24mm." whoop.in
3. WHOOP 5.0 SportFlex and CoreKnit product pages, official India storefront, same sizing line verbatim on each (one size, max 9.5 in / 24 cm, 24mm width). whoop.in SportFlex, whoop.in CoreKnit
4. WHOOP 5.0 CoreKnit Bicep Band product page and size chart, official India storefront: "S/M fits bicep circumferences between 10-13 in. L/XL fits bicep circumferences between 13-16 in." with the metric table 25-28 / 28-41.5 cm and the relaxed-arm measuring instruction. whoop.in
5. WHOOP 4.0 bicep band sizing guide, archived first-party shop page (2020): S/M 12 in / 30.5 cm, L/XL 17 in / 43.2 cm. shop.whoop.com via Wayback Machine
6. WHOOP shop 4.0 HydroKnit Bicep Band listing, archived official product page (S/M and L/XL size swatches on the 4.0-era shop), corroborated by the archived WHOOP 4.0 SuperKnit Bicep Band product data showing the same two-size option set. shop.whoop.com via Wayback Machine
7. WHOOP shop 5.0 LeatherLuxe Straight Band listing (S/M and L/XL size options; no wrist ranges printed first-party). shop.whoop.com
8. WHOOP community thread with a WHOOP Team answer (May 2025): "Due to updates in the hardware and a new shape, WHOOP body items and battery packs from 4.0 are no longer compatible with 5.0." community.whoop.com
9. WHOOP support, Band & Accessory Compatibility (article overview confirmed live; full body renders only in a browser as of build date): 4.0 bands, battery pack and apparel not compatible with 5.0/MG. support.whoop.com
10. WHOOP Podcast write-up with Founder/CEO Will Ahmed and CPO Ed Baker (May 2025): 5.0 and MG both 7% smaller than 4.0 with 14+ day battery, new Wireless PowerPack, and the MG scalloped clasp that carries the ECG contact points. whoop.com
11. WHOOP community staff answer, 5.0 & MG bands compatibility: 5.0 bands physically fit MG but disable ECG; strain, sleep and recovery unaffected. community.whoop.com
12. WHOOP support, WHOOP Basics: 5.0 measures 34.7 mm long, 24 mm wide, 10.6 mm high, weighs 26.5 g, about 7% smaller than 4.0. support.whoop.com
13. WHOOP accessories guide (whoop.com): per-band setup instructions, "snug but not too tight ... if you can fit a finger underneath, it's too loose" for SuperKnit, CoreKnit, SportFlex, CloudKnit and bicep bands. whoop.com
14. WHOOP support, Changing Bands with the Fast Link Slider: attach steps, "4.0 and WHOOP 5.0/MG bands are not cross-compatible", per-generation Fast Link designs, and "snug but comfortable fit ... about 1 inch away from the wrist bone." support.whoop.com
15. Independent WHOOP 5.0 review quoting WHOOP's support figures for the sensor: approximately 34.7 x 24 x 10.6 mm, about 26.5 g, and noting 4.0 battery packs are incompatible with 5.0 and MG. rottenwifi.com