Choose an armband by device, fastening style and upper-arm size. Measure the intended wearing position with a soft tape, then bend and relax your arm to check that the band can stay comfortable as you move.
Confirmed dimensions and estimated fit
Strap length is measured along the open band. Arm circumference is measured around your arm. They differ because a fold-back fastening needs an overlap and the device or connectors affect the closed loop.
The non-elastic ranges below are provisional geometric estimates, not physically tested fit ranges. We reserve approximately 5–6 cm (2.0–2.4 in) for fastening and allow for fold-back geometry. The exact usable range depends on connector routing and hook-and-loop placement; contact us with your measurement if you are near a limit.
| Armband | Open strap length | Estimated upper-arm circumference |
|---|---|---|
| Hume 2.0 SoftLoop | 42 cm / 16.5 in | 22–36 cm / 8.7–14.2 in |
| Fitbit Air Nylon | 40 cm / 15.7 in | 21–34 cm / 8.3–13.4 in |
| Amazfit Helio Nylon | 42 cm / 16.5 in | 22–36 cm / 8.7–14.2 in |
| WHOOP 5.0/MG Nylon | 42 cm / 16.5 in | 22–36 cm / 8.7–14.2 in |
| Garmin CIRQA Nylon | 43 cm / 16.9 in | 23–37 cm / 9.1–14.6 in |
| Apple Watch | 37 cm / 14.6 in | 22–35 cm / 8.7–13.8 in |
The elastic Hume 2.0 band and the two elastic WHOOP 5.0/MG bands use the separately supplied sizing: 35 cm (13.8 in) band length and 20–42 cm (7.9–16.5 in) arm circumference. Do not transfer an elastic band's range to a non-elastic model.
Apple Watch: include the watch body
The Apple Watch strap is 37 cm (14.6 in) long. Add approximately 3.8–4.9 cm (1.5–1.9 in) for the watch body, depending on case size: approximately 40.8–41.9 cm (16.1–16.5 in) before fold-back and fastening overlap. This supports the conservative estimated guide of 22–35 cm (8.7–13.8 in). Case height approximates the body contribution; connector geometry can change the final fit. See Apple's Series 10 dimensions.
Fit and fastening checks
- Confirm your exact device and connector before selecting a band.
- Measure your arm where you will wear it, including when bent.
- Thread the free end through the return loop and lay it flat, without twists.
- Fasten with sufficient hook-and-loop contact. Do not rely on a narrow edge of contact.
- Move your arm and check that the device stays in place comfortably. Follow the device maker's placement guidance.
Upper-arm placement can affect supported measurements and functions. Apple Watch is designed for wrist wear; this accessory does not guarantee wrist detection, heart-rate, ECG or other features on the upper arm.
Compare wearing solutions
Choose a hybrid band to combine a smartwatch and screen-free tracker on one wrist, or compare armbands and bicep bands for an upper-arm setup. For device-specific attachment choices, use the compatibility guide. Ask SYNCRBAND for fit help if you are unsure.
Prepared by SYNCRBAND Team. Updated October 31, 2026. Estimates use the stated strap dimensions and the assumptions above; they are not a substitute for physical fitting.