If you are stuck on what size pilates ball to buy before you hit checkout, relax, because this is one of the easier fitness decisions you will make today. The short version: the little soft pilates ball (the squishy one you tuck behind your back or squeeze between your knees) barely changes with your height, while the big inflatable gym or swiss ball absolutely does. Muddle the two up and you end up trying to squeeze a space hopper between your thighs. Let us sort it in a couple of minutes.
TL;DR
- Small soft pilates ball (the mini or "over" ball): usually 18cm to 25cm. Height barely matters. Pick by use and comfort. Our flexa.fit pilates ball is 18cm, the sweet spot for most people.
- Big gym or swiss ball (the one you sit on): size is all about your height. 45cm if you are under 5ft, 55cm for 5ft to 5ft 5in, 65cm for 5ft 6in to 6ft, 75cm for 6ft 1in and up.
- The golden rule for the big one: sit on it and your hips and knees should both sit at roughly 90 degrees, thighs level with the floor.
- The golden rule for the little one: part-inflate it so it is soft and squeezy, not rock hard. You want give.
- Two different tools: the mini ball is a prop you press against your body, the big ball is a platform you balance on. Do not size one like the other.
First, which "pilates ball" do you actually mean?
Here is the sneaky bit nobody warns you about. "Pilates ball" gets used for two totally different pieces of kit, and they are sized in totally different ways.
The small pilates ball goes by a lot of names: mini ball, soft ball, over ball, barre ball, even "that squishy one from class". It is small, soft, deflatable and lives between your knees, behind your lower back, or under your hips to add a little challenge or a little support. This is what most pilates instructors mean when they say "grab your ball".
The large ball is the big inflatable you sit or lie on. You will see it called a gym ball, swiss ball, stability ball, exercise ball or birthing ball. It is firm, it is huge, and you balance on top of it rather than pressing it into your body.
Nail down which one your class or workout means, because the sizing advice below splits right here.
What size for the small soft pilates ball?
Good news: this is the low-stress option. Small pilates balls typically run from 18cm to 25cm across, and your height is almost irrelevant. A 6ft 4in rugby prop and a 5ft 1in yoga fan can happily use the exact same 18cm ball. What actually matters is what you want it to do and how it feels under your body.
How to pick your soft ball by use
- 18cm to 20cm: the do-it-all size. Small enough to squeeze between your knees or ankles, comfy behind the lower back, and easy to pack. If you are buying your first one, start here. This is exactly why our flexa.fit pilates ball is 18cm.
- 23cm to 25cm: a touch bigger for a deeper stretch over the ball, more support under the hips in bridges, or if you simply prefer a larger prop to hug. Some taller folk like the extra size behind the spine.
That is honestly the whole decision. When a ball is this soft and part-inflated, it moulds to you, so there is no "wrong height". If in doubt, 18cm is the crowd-pleaser.
The soft, squeezy over-ball that fits behind your back, between your knees, and in your gym bag. The size most people should start with.
£5.99
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Give it a go (soft ball, 2 minutes)
- Inner-thigh squeeze: lie on your back, knees bent, ball between your knees. Squeeze for 5 seconds, release. Do 10 reps. You will feel your inner thighs and deep core switch on.
- Lower-back support: sit tall against a wall with the ball behind your lower back. Gently press back into it for 5 seconds, 8 times, to wake up your posture.
Want more where that came from? Our beginner pilates curl-ups guide pairs perfectly with a soft ball.
What size for the big gym or swiss ball? (this is where height matters)
Now the sizing actually earns its keep. With a big ball you are balancing on top, so getting the height right keeps your joints happy and your core doing the work instead of your lower back. The test is simple: sit on the fully inflated ball with your feet flat on the floor. Your hips and knees should both land at roughly 90 degrees, with your thighs parallel to the floor or tilting very slightly down. Too low and you are folded up like a deckchair. Too high and you are perched on tiptoes.
Gym ball size by height (the quick chart)
| Your height | Gym / swiss ball size |
|---|---|
| Under 5ft 0in (under 152cm) | 45cm |
| 5ft 0in to 5ft 5in (152cm to 165cm) | 55cm |
| 5ft 6in to 6ft 0in (165cm to 183cm) | 65cm |
| 6ft 1in and above (185cm and up) | 75cm |
One honest caveat: if you have long legs for your height, or plan to use the ball as a desk chair, size up a notch for comfort. Our flexa.fit gym ball comes in all four sizes with a pump in the box, so you can match your height without hunting for one separately.
Four sizes so you can pick by height, anti-burst for peace of mind, and the pump is already in the box. Sit, balance, plank and roll.
From £9.99 (45cm), up to £12.99 (75cm)
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Ready to put it to work once it arrives? Our gym ball exercises guide has plenty to try, and the exercise ball for pilates post covers how the big ball fits into a pilates routine.
Small pilates ball vs large gym or swiss ball: which do you need?
Short answer: possibly both, but they do different jobs, so buy for the job in front of you.
| Small pilates ball | Large gym / swiss ball | |
|---|---|---|
| Size | 18cm to 25cm | 45cm to 75cm |
| Feel | Soft, squeezy, part-inflated | Firm, fully inflated |
| How you use it | Press it into your body as a prop | Balance on top of it as a platform |
| Best for | Core squeeze work, pelvic floor, gentle spine mobility, added support | Balance, whole-body stability, big-range core work, active sitting |
| Sized by | Use and comfort (not height) | Your height |
| Portability | Deflate and pocket it | Stays inflated, lives in a corner |
If your class notes say "pilates ball" or "soft ball", grab the little one. If they say "swiss ball", "stability ball" or "exercise ball", you want the big one and you want to size it by your height. Plenty of home setups end up with both, because a soft ball for targeted core work and a big ball for balance and posture is a brilliant, low-cost combo.
Inflation tips (so it feels right, not rock hard)
Getting the air right matters more than people think, and the two balls want opposite things.
Soft pilates ball
- Underinflate on purpose. You want it soft and yielding, roughly 80 to 90 percent full, so you can compress it. A rock-hard mini ball is uncomfortable and defeats the point.
- Use the little plug or a balloon pump. Most soft balls come with a small straw or plug. Pop it in, add a few puffs, test the squish, top up if needed.
- Let it settle. Give it a minute, then adjust. When you press it, it should give a good couple of centimetres without any strain.
Large gym or swiss ball
- Inflate in two stages. Pump to around 80 percent, then leave it for a day so the material can stretch. Top it up to full the next day. This is the trick to a ball that holds its shape and size.
- Measure, do not guess. Stand the ball on the floor and check its height against a wall. A 65cm ball should measure about 65cm tall. Mark 65cm on the wall with a bit of tape and inflate until the top reaches it.
- Do not overfill. Anti-burst is a safety net, not a licence to cram in extra air. Overinflating makes the ball too firm to balance on and stresses the seams. If the surface looks tight and shiny with no give at all, let a little out.
- Top up now and then. Balls lose a bit of pressure over weeks. A quick re-check keeps the height, and your posture, correct.
Do not forget the floor
Whichever ball you go for, a decent mat makes all the difference. Soft-ball core work happens lying down, and kneeling around a big ball is far kinder on your knees with cushioning underneath.
Cushioned, grippy and rolls up with a strap. The everyday floor for soft-ball core work.
£12.99
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Extra-thick 8mm cushioning for sensitive knees and longer floor sessions. Your joints will thank you.
£24.99
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Building a home setup from scratch? Browse the whole yoga and pilates collection to grab your balls and mat in one go.
FAQs
What size pilates ball do I need for beginners?
For the small soft pilates ball, start with 18cm to 20cm. It is comfortable behind the back, easy to squeeze between the knees, and suits almost everyone regardless of height. If you mean the big swiss ball, size it by height instead: most adults between 5ft 6in and 6ft want a 65cm ball.
Does my height change what size pilates ball I need?
Only for the big gym or swiss ball, where height decides everything. For the small soft pilates ball, height barely matters because it is soft and moulds to your body. A tall person and a short person can share the same 18cm soft ball with no issue.
What is the difference between a pilates ball and a swiss ball?
A pilates ball usually means the small, soft, deflatable ball (18cm to 25cm) that you press into your body as a prop. A swiss ball, also called a gym or stability ball, is the large firm one (45cm to 75cm) you sit or balance on. They are sized in completely different ways, so check which your class means.
How firm should my pilates ball be?
The small soft ball should stay squishy, around 80 to 90 percent inflated, so you can compress it during exercises. The large swiss ball should be firm and hold its round shape, but never so tight it has no give at all. Match the ball's stated size when you inflate the big one.
Can I use a gym ball instead of a small pilates ball?
Not really, as they do different jobs. A gym ball is a platform you balance on, so it cannot slot between your knees or sit behind your lower back the way a soft pilates ball does. If your routine calls for a small over-ball, you will want the little soft one. Many people keep both.
How do I know if my swiss ball is the right size once it is inflated?
Sit on it with feet flat on the floor. Your hips and knees should both sit at roughly 90 degrees and your thighs should be parallel to the floor. If your knees are higher than your hips, the ball is too small. If you are on tiptoes, it is too big or overinflated.
Conclusion: pick your ball in 30 seconds
So, what size pilates ball do you need? If it is the small soft one, keep it simple and go 18cm to 20cm, choosing by feel rather than height. If it is the big gym or swiss ball, let your height do the choosing: 45cm, 55cm, 65cm or 75cm as you go up the chart, and always double-check with the sit test where your hips and knees land at 90 degrees. Inflate the soft ball squishy, inflate the big one firm and to size, and you are ready to roll. Grab a soft pilates ball, a right-sized gym ball, and a comfy mat, and your home core setup is basically sorted.
A quick note: this is general fitness guidance, not medical advice. If you are pregnant, recovering from an injury, or have any pain that lingers, check in with a GP or physio before starting something new. The NHS has friendly, free reading on staying active and the weekly activity guidelines for adults if you want a sensible baseline.
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