Getting a new smart watch strap should be a painless experience, but there’s one thing that causes pause time and time again: watch sizing.
In this guide we’re going to simplify watch strap selection. By breaking down the difference between band size and case size, we can clear up the 45mm vs 46mm confusion for good.
Here’s the thing, a 45mm strap can sometimes fit a 46mm smart watch, but case size alone doesn’t determine compatibility. Lug width and connector type determine whether a replacement band actually fits.
Most brands, including Garmin and Samsung, can change lug width or connector systems between generations, even when case sizes stay nearly identical. Apple Watch is the one notable exception, having kept its connector system consistent across various different case sizes.
Key Takeaways
- Case size refers to the diameter of the watch face, not the width of the band. It doesn’t tell you what band will fit.
- Lug width and connector type determine whether a replacement band fits.
- A “45mm band” label usually refers to the watch case size that the band fits, not the physical band width.
- Garmin and Samsung watches can change lug widths or connector systems between generations, even when case sizes stay similar.
- Apple Watch is an exception: 45mm and 46mm bands are cross-compatible because Apple kept the same connector system when the case size grew.
- Always confirm compatibility using lug width and connector type before ordering a replacement strap.
Case Size and Band Size Are Different Measurements
To find your smart watch band size, you need to know the difference between case size and lug width. They’re separate measurements.
Case size is the diameter of the watch face. Lug width refers to the distance between the two band attachment points on the case and determines whether a replacement strap fits correctly. Mixing up case size and lug width is where most orders go wrong.
These sizes are set by manufacturers independently. A 46mm smart watch can use either a 20mm or 22mm lug width, depending on the model, which is why two similarly sized watches can require completely different bands.
| Term | What It Measures | Example |
|---|---|---|
| Case size | Diameter of the watch face | 44mm, 45mm, 46mm |
| Lug width | Gap between the band attachment points | 20mm, 22mm |
Therefore, when you see a product listing labeled “45mm band”, it usually means the band fits a 45mm smart watch case. The physical band width is a separate measurement.
Why Case Size Alone Can’t Tell You If a Band Fits
Because most manufacturers change lug width or connector systems between models, even when the case size looks the same, the case size on the box is rarely enough information on its own. Here’s how that plays out across major brands.
Samsung
Samsung Galaxy Watch models are a good example of how case sizes don’t determine lug width. The 46mm Galaxy Watch used a 22mm lug width, while the Samsung Galaxy Watch 4 Classic 46mm switched to a 20mm lug width.
Same case size. Different band sizes. A strap from one won’t fit the other.
Garmin
Garmin watches add a second factor to compatibility. Some of their devices share the same lug width, but use different connector systems. While various Garmin models use standard Quick Release connectors, Garmin also has their own proprietary connector: Garmin’s QuickFit.
A Garmin QuickFit 22 band won’t fit other Garmin watches with a 22mm Quick Release setup.
Apple
Apple Watches are an exception to typical sizing guidelines. They sidestep the lug width measurement altogether.
Instead of spring bars and lugs, Apple Watch bands click into a proprietary connector, and compatibility is grouped by connector family rather than by millimeter measurement: a “small” family covering the 38mm, 40mm, and 41mm cases, and a “large” family covering 42mm, 44mm, 45mm, and 46mm cases (plus the 49mm Ultra).
Because Apple kept the same connector across the “large” family, a 45mm Apple Watch band fits Series 7, 8, and 9 as well as the 46mm Series 10 and 11. The same connector also reaches back to the 44mm bands from Series 4, 5, and 6, too.
That cross-compatibility holds across sport bands, leather bands, braided straps, and metal bands alike.
One caveat: Series 10 and 11 also come in a smaller 42mm case that belongs to the 38–41mm band family instead, so always confirm the case size, not just the series.
Overall, you should never assume two watches use the same bands because the case sizes look similar, always confirm compatibility before committing to a new smart watch strap.
How to Confirm Band Compatibility Before Ordering
There are two quick methods to confirm compatibility before ordering a replacement band:
Method 1: Check the Case Back
- Turn the watch face down.
- Look near the lug openings or the connector area for a millimeter measurement.
- The printed number usually indicates your lug width.
Method 2: Check the Product Specifications
- Find the full watch model name from the case back or device settings.
- Check the manufacturer’s compatibility specifications for the confirmed lug width and connector type.
Shopping by Lug Width Instead of Case Size
So, does a 45mm strap fit a 46mm smart watch? Ultimately, the answer depends entirely on the lug width and/or connector type, not the case size printed on the box.
StrapsCo bands are organized by lug width to remove the guesswork.
Browse QuickFit 22 watch bands or QuickFit 20 watch bands depending on your confirmed measurement, or use our Garmin lug width guide, which covers popular models, including the Fenix 7, Epix Pro, Forerunner 965, Venu 3, and Instinct 2.
Shopping for a Samsung Galaxy Watch strap? Double-check your specific model’s lug width before ordering, since it can change between generations even when the case size stays the same.
And if you’re after a band for your Apple Watch, look for the connector family it belongs to (38/40/41/42mm or 42/44/45/46/49mm) rather than the case size alone, that’s the number that actually determines fit.
Remember, lug width and connector type are what actually fit your wrist. Once you’ve confirmed those, replacing a strap is genuinely easy. Check the case back, match the lug width (or connector family, for Apple), and order with confidence.
What smart watch are you trying to find the perfect band for? Let us know in the comments or reach out to our team, we’re happy to help you track down the right fit.
Frequently Asked Questions (FAQs)
Does a 44mm Apple Watch band fit a 45mm Apple Watch?
Yes. Apple Watch 44mm bands from Series 4, 5, 6, and SE are compatible with 45mm Apple Watch models (Series 7, 8, and 9) as well as the 46mm Apple Watch Series 10.
Apple bumped the case from 44mm to 45mm with the Series 7 in 2021, then to 46mm with the Series 10 in 2024, but it kept the same band connector, so bands fit these generations interchangeably.
What is the difference between a 45mm and a 40mm Apple Watch band?
The difference comes from the connector size group, not the physical width of the band.
Apple sorts its watches into two families: a larger group and a smaller group.
A 45mm Apple Watch band fits 44mm, 45mm, and 46mm Apple Watch cases. A 40mm Apple Watch band fits 38mm, 40mm, and 41mm Apple Watch cases. The two groups use different connector dimensions and are not cross-compatible.
Does lug width apply to Apple Watch bands?
Not in a traditional sense. Apple Watch uses a proprietary sliding connector system instead of traditional spring bar lugs.
Apple’s larger (44/45/46mm) and smaller (38/40/41mm) size groups function as the compatibility system instead of standard lug widths like 20mm or 22mm.
Traditional lug width measurements apply to Garmin watches, Samsung Galaxy Watch models, and classic watches that use spring bar connections.
Does a Garmin QuickFit 22 band fit a watch with a standard 22mm Quick Release lug?
No. Even though both measure 22mm, QuickFit and Quick Release are different connector systems, not just a width match.
QuickFit bands use a locking lever that snaps into a specific mechanism on the smart watch case, while Quick Release bands use a spring bar released with a small pin.
The two aren’t interchangeable, so always confirm which connector type your specific Garmin model uses, not just the lug width.
Do all 46mm Samsung Galaxy Watch models use the same band?
No. The original 46mm Galaxy Watch uses a 22mm lug width, but the Samsung Galaxy Watch 4 Classic 46mm switched to a 20mm lug width — same case size, different band.
Because Samsung has changed lug width between generations even at the same case size, always confirm your specific model’s lug width before ordering rather than assuming based on the case size alone.
