What are the Different Sizes of Apple Watch Strap by Series?

Buying a new strap should feel like choosing a new outfit... not decoding a secret Apple code. Yet, one search for an apple watch band size mm chart quickly turns into: 38, 40, 41, 42, 44, 45, 46, 49… and a mild desire to lie down!

Here’s the good news: Apple Watch bands mostly live in two compatibility families, and once you know which family your case belongs to, the rest becomes surprisingly simple. Even better, with this guide you can double check your case size and avoid that dreaded “nearly-right” strap.

In this guide from The Thrifty Gentleman, we’ll walk you through:

1. a clear Apple Watch band size chart in mm;
2. strap sizes by series, including the confusing “42mm” naming overlap;
3. how to measure your wrist properly, and
4. "Apple Watch style and comfort tips" for choosing bands that actually suit UK life - commutes, coffees, workouts, and nights out.

A Few Early Tips to Get Us Started

• Apple Watch bands mainly fall into two size families: Small (38/40/41/42) and Large (42/44/45/46/49)
• 46mm cases can use bands from our 42/44/45/46/49 range, and 49mm (Ultra) can use the same 42/44/45/46/49 range in many cases.
• The “42mm” label can mean two different families depending on the series (older Series 1 - 3 vs newer Series 10/11). More to follow on that but with our watch straps you can clearer see which straps are for the Series 10 and 11 and which are for the earlier series.
• For the best fit, measure your wrist in mm and match band type (Solo Loop vs Sport Band, etc.). We include fit in all of our product specifications.
• If you’re between sizes, comfort usually wins: a slightly snug Solo Loop is fine; a too-tight metal link is not.
• UK pro tip: cold weather swelling is real so leave a touch of breathing room for autumn/winter.
• Your “perfect” strap is about case compatibility, wrist sizing and lifestyle (gym, office, weekends) so take them all into consideration when choosing your strap.

Apple Watch Band Size Chart in mm (the Simple Compatibility Rules)

If you only read one section, make it this one. The fastest way to use an apple watch band size chart mm is to ignore the marketing names and focus on case size family.

The Two Main Band Families

Apple’s official guidance boils down to two core groups:

• Small family: 38mm / 40mm / 41mm cases (and some newer 42mm, explained below) share bands.
• Large family: 42mm / 44mm / 45mm cases share bands.

The Newer Crossover Sizes (46mm and 49mm)

Where it gets better (not worse!): Apple also states newer sizes work across the larger family:

• 46mm cases are compatible with 42mm, 44mm, 45mm, 46mm & 49mm bands.
• 49mm (Ultra) cases are compatible with 42mm, 44mm, 45mm, 46mm & 49mm bands and many 42 (larger Apple watch option)/44/45/46 cases can use 49mm bands too.

The Apple Watch Strap Size Chart By Series

Series	Smaller Strap Size	Larger Strap Size
Series 1	38mm	42mm
Series 2	38mm	42mm
Series 3	38mm	42mm
Series 4	40mm	44mm
Series 5	40mm	44mm
Series 6	40mm	44mm
Series 7	41mm	45mm
Series 8	41mm	45mm
Series 9	41mm	45mm
Series 10	42mm	46mm
Series 11	42mm	46mm
Series SE	40mm	44mm
Ultra 1	N/A	49mm
Ultra 2	N/A	49mm

Quick “Pick the Right Size” Checklist

1. Flip your watch over and find the case size in mm.
2. Match it to the Small or Large family using the bullets above.
3. Only then think about band type (Solo Loop, Sport, Milanese, etc.).

Why Apple Keeps it This Way

Competitor guides often treat this like chaos but it’s actually a strategy: Apple protects band longevity. By keeping families compatible across multiple generations, your strap wardrobe can outlive your Watch upgrade. That’s brilliant for sustainability and for your style rotation especially if you’re the type to match straps to outfits. Are Apple Watch straps expensive? Of course! But that is a way in which Apple allow you to "transfer" those straps from your old watch to your new.

It works in exactly the same way with the third party Apple compatible straps we sell too though so you can do exactly the same thing with straps from The Thrifty Gentleman.

(And yes, we’ll still handle the “42mm” curveball next.)

Strap Sizes by Series: Which Apple Watch Models Use Which Bands?

This is where most guides get vague. Let’s be specific, using Apple’s own sizing data points and reputable model tables.

Case Sizes You’ll See Most Often (by era)

• Series 3 and earlier: Apple Watch came in 38mm and 42mm.
• Series 4: Case sizes shifted to 40mm and 44mm.
• Series 7: Case sizes became 41mm and 45mm.
• Series 10/11 era: Commonly listed as 42mm and 46mm in current buyer comparisons.
• Ultra line: 49mm case size, designed around rugged straps and wider lugs.

The “42mm” Confusion (Old vs New)

Here’s the trap: “42mm” can refer to two different things depending on the generation.

Some charts explicitly warn that Series 1 - 3 “42mm” belongs to the Large family, while newer “42mm” (Series 10/11 era) may belong to the Small family.

How to Avoid Buying the Wrong “42mm” Band

If your watch is Series 1 - 3, your 42mm is the Large family (bands labelled 42/44/45/46/49 often fit).

If your watch is newer (Series 10 and 11) and says 42mm, treat it like the Small family unless the retailer explicitly states otherwise. Cross-check the product listing’s compatibility notes before buying and check it against the chart we have provided above.

UK Shopping Shortcut

When browsing The Thrifty Gentleman's online strap store, look for selectors written like:

“38/40/41mm & 42mm (Series 10 & 11)” (small family)

“42/44/45/46/49mm” (large family)

That formatting is the popular choice by us here because it mirrors the real-world buying decision (compatibility family), not just one single size label.

Measure Your Wrist in mm: Getting the Perfect Fit (especially for the Elastic Solo Loop)

Compatibility gets the strap onto your Watch. Wrist sizing determines whether it feels like tailored or torture!

Wrist Measurement Tips That Actually Work

• Measure at the time you wear it most. If you’re buying a “daily” strap, measure in the afternoon - wrists tend to be slightly larger later in the day.
• Keep it snug, not strangled. You want “doesn’t slide up/down,” not “leaves a dent.”
• Account for seasons (UK reality check). In colder months, you may prefer one notch looser on Sport Apple Bands; in summer, sweaty swelling can do the opposite.

Band-Type Sizing: Why the Elastic Solo Loop Feels Different

Some bands are forgiving; others are not:

Sport Band / Sport Loop: adjustable and easy - great if your wrist fluctuates.

Solo Loop / Braided Solo Loop: minimal adjustability, so measurement matters more.

Modern Buckle: comes in multiple wrist-range sizes; some guides note it’s offered in specific mm ranges (useful if you’re between fits).

Unique Insight: “Comfort Fit” Beats “Spec Fit”

Most competitors chase a single “correct” number. In practice, you want the strap to behave as it does in real life:

• On a commute, your strap shouldn’t slide when you grab the rail.
• In a workout, it shouldn’t cut off circulation when your heart rate climbs.
• At a desk, it shouldn’t press the sensor away from skin.

Choosing The Right Strap: Comfort, Style, and “UK Life” Practicality

Now for the fun part... because straps aren’t just functional. They’re one of the easiest ways to make your Watch feel like yours.

Quick Style Matching (Gender-Neutral, Outfit-Friendly)

• Minimalist daily: matte silicone or a sleek Milanese-style mesh for an “always works” look.
• Soft luxe: leather-style straps for dinner plans and office days (pairs well with coats, knitwear, and jewellery).
• Sporty: breathable sport loops for gym sessions, runs, and weekend walks.

Activity-Based Recommendations

Several ranking guides frame strap choice around use cases - silicone for workouts, leather/metal for office, rugged loops for outdoors.

That’s solid advice, but here’s the upgrade:

Unique Insight: Build a “Three-Strap Wardrobe”

Instead of chasing one strap to do everything, aim for:

1. Daily strap (comfort-first)
2. Workout strap (washable, breathable)
3. Dress-up strap (texture/metal/leather look)

It’s cheaper long-term than repeatedly buying “almost right” straps and it makes your Apple Watch feel like a proper accessory, not just a gadget.

Make the Chart Work for You (Not Against You)

Whenever you’re unsure, return to the rule: case family first. Apple’s compatibility bullets are the anchor that keeps you from ordering the wrong connector size.

And if you’re buying for someone else (gift season, birthdays, “I saw this and thought of you”), ask for a photo of the back of their Watch. The case size in mm is your golden ticket into the right watch strap family.

Conclusion

If Apple Watch strap sizing has ever made you feel like you need a maths degree, you’re not alone. The secret is that the apple watch band size chart in mm isn’t really about memorising every number, it’s about recognising compatibility families.

Start with the back of your Watch: find the case size in mm and match it to the right group. Apple’s official guidance makes it clear that 38/40/41/42 share bands, 42/44/45 share bands, and newer sizes like 46mm and 49mm (Ultra) often work across the larger family too.

Then dial in comfort by measuring your wrist in mm, especially if you’re choosing an Elastic Solo Loop style where sizing is less forgiving.

Finally, remember straps are style. Build a small rotation (daily, workout, dress-up), and your Apple Watch instantly becomes more personal.

It's like swapping trainers for boots depending on where the day takes you!

Frequently Asked Questions (FAQs)

1) What size Apple Watch strap do I need?

Check the mm size on the back of your Watch, then match it to the correct family in an apple watch band size chart in mm: small (38/40/41/42 (Series 10 or 11) or large (42/44/45), with 46/49 often compatible with the larger family.

2) Do 40mm and 41mm Apple Watch bands fit the same?

Yes - Apple states bands for 38mm, 40mm, and 41mm and the newer 42mm cases are compatible with each other.

3) Will a 44mm band fit a 45mm Apple Watch?

Yes - Apple states 42mm, 44mm, and 45mm cases share band compatibility.

4) Can Apple Watch Ultra (49mm) use regular bands?

Often, yes and in the case of the straps here at The Thrifty Gentleman, yes. Apple says 49mm cases are compatible with 42mm (older versions), 44mm, 45mm, or 46mm bands (and vice versa in many cases).

5) I have a 42mm Apple Watch. Why do some bands not fit?

Because “42mm” can mean different generations. Older Series 1 - 3 (42mm) align with the large band family, while newer 42mm models align with the smaller strap family. Therefore, always check series compatibility notes before you buy.