Search for a yoga ball and you will be shown two completely different products: a large inflatable ball somewhere between 45 and 85cm across, and a small soft ball about the size of a honeydew melon. They do different jobs and suit different patients. This guide is for UK physiotherapists, rehab clinics, Pilates studios and home users who need to work out which one they meant before they order the wrong one.
TL;DR
- A yoga ball, gym ball, Swiss ball, stability ball, exercise ball, physio ball and birth ball are all the same thing: the large inflatable ball, usually 45 to 85cm.
- A pilates ball in UK retail usually means the small soft ball, roughly 18 to 25cm, that you squeeze between the knees or place under the lower back.
- Oxford Health NHS Foundation Trust sizes the large ball by height, from a 45cm junior ball under 150cm tall up to an 85cm ball above 198cm.
- Two different sitting rules exist, both from the NHS. For exercise, hips and knees at right angles. For labour, knees about 10cm lower than the hips.
- Anti-burst means the ball deflates slowly when punctured instead of popping. It is a failure mode, not a strength rating.
- Sitting on one at a desk all day has weak evidence behind it. A 2009 study found more lumbar muscle activity and more spinal shrinkage than an office chair.
- Meglio's Anti-Burst Gym Ball starts at £7.49 ex VAT for the 45cm and is £9.16 ex VAT for the 65cm. The 18cm Pilates Ball is £6.66 ex VAT, or £4.66 each when you buy 30 or more.
Why the naming is such a mess
The large ball was never given one agreed name. It picked up a different label in every setting it landed in, and none of them ever won. In physiotherapy departments it is a Swiss ball, in gyms an exercise ball or a stability ball, in yoga and Pilates studios a yoga ball. Maternity units know it as a birth ball, while procurement catalogues tend to list it as a gym ball.
Oxford Health NHS Foundation Trust puts it plainly in its children's therapies leaflet, which opens by defining a gym ball as a ball "also called Swiss ball, exercise ball, yoga ball or stability ball" and describes it as a large ball made of plastic vinyl and elastic and filled with air. That is one NHS trust listing four names for a single product in a single sentence, which tells you how settled the terminology is.
The complication is the word "pilates". Older reference material lists "pilates ball" as yet another name for the big ball. UK retail has since drifted the other way, and a search for a pilates ball today mostly returns the small soft ball used in mat classes. So "pilates ball" is the one name in the list that genuinely points at two different products depending on where you read it. Everything else in the list means the big ball.
Is a yoga ball the same as a gym ball?
Yes. A yoga ball and a gym ball are the same product with two names, and neither term describes anything the other does not. The same applies to Swiss ball, stability ball, exercise ball, physio ball and balance ball. If a supplier lists a yoga ball at 65cm and a gym ball at 65cm, you are looking at the same item twice.
Where the names carry real information is in the intended use, and that changes what you should check before buying. A ball sold as a birth ball should be anti-burst and non-slip because it will be used by someone heavily pregnant on a hospital floor. A ball sold for a clinic gym needs to survive being wiped down several times a day. The ball itself is the same object, so read the specification rather than the label.
The pilates ball is a different product entirely
The small ball is soft, deliberately underinflated, and used against the body rather than under it. It goes between the knees for adductor work, under the sacrum for pelvic tilts, behind the lower back against a wall, or between the hands for shoulder cues. It is not a scaled-down gym ball. You cannot sit on it, and the exercises do not transfer.
Sizes run from about 18cm to 25cm, which is where the imperial listings come in: a 7 inch ball is roughly 18cm, a 9 inch ball is roughly 23cm, and a 10 inch ball is about 25cm. Smaller balls give a firmer squeeze and are easier for patients with limited hip range to hold. Larger ones give a softer, longer range of movement. Our clinical guide to using a pilates ball covers the graded exercises and hygiene cues in more depth.
Ball naming and size table
| What people search | What it means | Typical size |
|---|---|---|
| Yoga ball | The large inflatable ball | 45 to 85cm |
| Gym ball, Swiss ball, stability ball, exercise ball, physio ball | Same large ball, named after the setting it is used in | 45 to 85cm |
| Birth ball, birthing ball | Same large ball, used in pregnancy and labour | 65 or 75cm |
| Pilates ball, soft ball, mini ball, over ball | Small soft ball, squeezed or placed under the body | 18 to 25cm |
| Balance trainer, wobble cushion | A domed half ball on a rigid base, or a small inflatable disc. Different products again, and no substitute for either ball | Varies by brand |
What size yoga ball do I need
Size the large ball by the height of the person using it. Oxford Health NHS Foundation Trust publishes a height chart in its gym balls leaflet, and it is the cleanest UK reference because it works in centimetres rather than feet and inches.
| Height of user | Ball size |
|---|---|
| Under 150cm | 45cm (junior) |
| 150 to 165cm | 55cm (small) |
| 162 to 183cm | 65cm (medium) |
| 180 to 200cm | 75cm (large) |
| Over 198cm | 85cm (extra large) |
The bands overlap in places, at 162 to 165cm and again at 180 to 183cm, so around those heights either size sits within the chart. The tie-breaker is leg length and what the ball is being used for. Someone at 164cm with long legs will be more comfortable on the 65cm.
The check that matters more than the chart is the sit test. Oxford Health's rule for exercise is that hips and knees should be at right angles with the feet flat on the floor. That is the position you want for bridging, seated bouncing, trunk rotation and anything where the ball is a load-bearing surface.
Labour is the exception, and the NHS gives a different rule for it. The NHS guidance on how to use a birthing ball says the knees should be about 10cm lower than the hips, which puts the pelvis in a more open, forward-tilted position. It recommends a 65cm ball up to 1.73m in height and a 75cm ball above that. If you are buying one ball to cover both antenatal classes and general rehab, size it for labour and accept the compromise on the exercise position.
How inflated should the ball be
Inflate to the stated diameter, not to the point where it feels firm. Firmness is a training variable, and Oxford Health's leaflet says it directly: the firmer the ball, the more difficult the exercise will be. A softer ball gives a larger contact patch, sinks more under load and is easier to control, which is what you want for an anxious patient or a first session.
The practical method is to mark the target diameter on a wall, inflate to roughly four fifths, leave it for a few hours so the material stretches evenly, then top it up to the mark. New balls stretch on first inflation, so a ball that measures correctly straight out of the box will read short a day later. Check it against the wall marks again before it goes into clinic use, then re-check every few weeks.
The small pilates ball works in the opposite direction. It is meant to be underinflated, usually somewhere between half and three quarters full, so it deforms when squeezed. A hard 18cm ball gives the patient nothing to work against and makes the adductor and pelvic floor cues almost impossible to feel.
What anti-burst means, and what it does not
Anti-burst describes how the ball fails, not how strong it is. The NHS birthing ball guidance defines it as material that "deflates slowly, rather than pops" when punctured, and notes that good quality birthing balls are pressure-tested to support weights up to 300kg. That distinction matters most for the people you would least want on a bursting ball: someone in late pregnancy, an older adult working on balance, or a patient in early post-operative rehab.
Oxford Health's leaflet applies the same standard to children's therapies, stating simply that the ball should be burst resistant. Treat anti-burst as a minimum specification for any clinical setting rather than a premium feature worth paying extra for. If a ball in your gym is not anti-burst rated, it should not be in a session with a patient who cannot get off it quickly.
One thing anti-burst does not do is protect against slow leaks from a poorly seated valve plug, or against the surface wearing smooth. A ball that has lost its texture is a slip risk long before it is a burst risk. Our UK anti-burst gym ball roundup goes further into burst ratings and what the numbers on the box mean.
What the evidence supports
The strongest evidence for the large ball is in maternity, not in the gym. A systematic review and meta-analysis of seven randomised controlled trials covering 533 women found that labour pain fell by 1.70 points in the birthing ball group compared with no ball, with no significant difference in rates of spontaneous vaginal delivery, operative delivery, caesarean or perineal tearing. The review looked specifically at women labouring without an epidural, so that is the group the finding applies to. The ball helped with pain in the first stage. It did not change how the birth went.
Antenatal use has support too. A study of 89 women in Taiwan, published in Midwifery, found that those who attended a 12 week stability ball exercise programme from around 20 weeks reported significantly less low back pain and less interference with daily life by 36 weeks than the control group. The study was non-randomised and controlled, so treat it as supportive rather than definitive.
Where the picture gets more honest is general core work. A randomised trial comparing Swiss ball training with static core exercises in 30 women with postpartum low back pain found both groups improved, with no significant difference between them. A 2022 meta-analysis in the Journal of Sports Sciences pooling 226 participants across ten studies found a moderate effect of core training on dynamic balance, and reported that body weight exercises may be better than medicine ball, Swiss ball or band resisted work for that outcome.
Read together, that says the ball is a delivery mechanism rather than an active ingredient. It makes certain exercises possible, gives a patient a target to work against and adds novelty that keeps people doing the programme. It does not beat well-prescribed floor work on its own merits, and any supplier telling you otherwise is selling.
Should you sit on a yoga ball at your desk
Probably not for a full working day, and the research is more discouraging than most product pages let on. A study in Applied Ergonomics monitored ten women through a one hour typing task, once on an office chair with armrests and once on an exercise ball. Sitting on the ball produced 33% more trunk motion and 66% more variation in lumbar muscle activity, which reads as a win. But average lumbar muscle activity was 78% higher, and there was more spinal shrinkage over the hour. The authors concluded that the advantages may not outweigh the disadvantages.
If a patient asks, the sensible advice is to use it in blocks rather than as a chair replacement. Twenty minutes at a time, alongside a proper chair, gets the movement variation without an hour of loaded lumbar erectors and nothing to lean back on. That is a useful line to have ready, because "sit on a gym ball instead of your chair" is still repeated as if it were settled advice.
Which ball to buy
Anti-Burst Gym Ball, the one people mean by yoga ball
This is the large ball, sold in 45cm, 55cm, 65cm and 75cm. Anti-burst construction with a textured, non-slip surface, and the four sizes cover the Oxford Health chart from junior through to 200cm tall. The 65cm is the one to order if someone typed "yoga ball" and meant it, because it fits the 162 to 183cm band that most adults sit in, and it matches the NHS birthing ball recommendation for anyone up to 1.73m.
Where it works well:
- Anti-burst across every size, so it is appropriate for antenatal classes and older adult balance work.
- Four sizes from one supplier, which keeps a clinic gym consistent instead of mismatched.
- Textured finish holds up to repeated wipe-downs between patients.
Where it falls short:
- No 85cm option, so anyone over about 198cm will need to look elsewhere.
- No volume discount tier on this product, so buying six for a clinic gym costs six times one.
Verdict: the default choice if you searched for a yoga ball, and the ball to put in a clinic gym or an antenatal group. Price is £7.49 ex VAT for the 45cm rising to £9.99 ex VAT for the 75cm, with the 65cm at £9.16 ex VAT.
Pilates Ball 18cm, the small soft ball
The 18cm soft ball is the smaller end of the Pilates range, which makes it the firmer squeeze and the easier one to hold for patients with restricted hip abduction. It suits adductor and pelvic floor cueing, supported bridging, seated posture work and thoracic mobility against a wall. It is easy to hold in one hand and takes almost no storage space, which is what makes it workable for group settings.
Where it works well:
- Underinflates well, so you can dial the resistance to the patient rather than the other way round.
- Small enough that a class of twelve stores in one crate.
- Volume pricing that makes sense for studios kitting out a whole class.
Where it falls short:
- Not a substitute for the large ball. If someone wants to sit or bridge on it, this is the wrong product.
- At 18cm it gives a shorter range of movement than a 23cm or 25cm ball, which some patients find harder to feel.
Verdict: the right ball for mat Pilates, women's health rehab and any clinic doing adductor or pelvic floor cueing. £6.66 ex VAT for a single, with volume tiers of 15% off at 10 or more and 30% off at 30 or more, which brings it down to £4.66 each. Our roundup of the best pilates balls in the UK compares it against the alternatives if you want the wider view.
Stocking a clinic or studio
A clinic gym does not need one of everything. Two 65cm balls and one 55cm cover most adult patients on the Oxford Health chart, with a 75cm added if you regularly see taller people or run antenatal groups where women want to choose. The 45cm is a paediatric and seated-transfer size rather than a general adult one.
For the small ball, buy per patient place rather than per therapist. A class of twelve needs twelve, which clears the 15% tier at 10 or more and brings the ball to £5.66 ex VAT. The 30% tier does not start until 30, so two classes of twelve still sit in the lower band. If you run a third class, or want the spare set that studios end up needing because balls get taken home and not returned, ordering 30 drops the per-ball price to £4.66 ex VAT.
Hygiene is the recurring cost nobody budgets for. Both balls are wipeable, but repeated alcohol wipes will dull a textured surface over time, and a smooth ball is a slip hazard. Check the grip with a flat palm every few weeks and retire the ball when it starts to feel slick, not when it starts to leak. Storage matters too: keep balls away from radiators and skirting board heaters, because heat and pressure together are what push a seam.
Both sit in the yoga and Pilates collection alongside mats and hot and cold packs if you are putting a full studio order together.
FAQs
Is a yoga ball the same as a pilates ball?
Usually not, in UK retail. A yoga ball is the large inflatable ball, typically 45 to 85cm, that you sit or lie on. A pilates ball in most UK listings is the small soft ball of 18 to 25cm that you squeeze between your knees or place under your back. Some older reference material does list "pilates ball" as another name for the large ball, which is where the confusion starts.
What size yoga ball do I need for my height?
Oxford Health NHS Foundation Trust's gym ball chart recommends 45cm under 150cm tall, 55cm from 150 to 165cm, 65cm from 162 to 183cm, 75cm from 180 to 200cm and 85cm above 198cm. The confirming check is to sit on it: your hips and knees should be at right angles with your feet flat on the floor.
Is a yoga ball the same as a Swiss ball?
Yes. Swiss ball, gym ball, stability ball, exercise ball, physio ball, balance ball and birth ball all describe the same large inflatable ball. The names come from the settings the ball was adopted in rather than from any difference in the product. An NHS children's therapies leaflet lists Swiss ball, exercise ball, yoga ball and stability ball as names for one item.
How do I know if my ball is inflated properly?
Measure it rather than judging by feel. Mark the stated diameter on a wall and inflate until the ball reaches the mark, leaving it a few hours part-inflated first so the material stretches evenly. New balls stretch and need topping up after a day. A firmer ball makes exercises harder, so a slightly softer ball is the safer starting point for a nervous patient.
Can I use a yoga ball as a birthing ball?
Yes, provided it is anti-burst and the right size. The NHS advises a 65cm ball up to 1.73m in height and 75cm above that, with the knees sitting about 10cm lower than the hips. It also says to only use a ball in labour if you have practised with it during pregnancy and feel steady on it.
Is sitting on a yoga ball at a desk good for your back?
The evidence does not support it as a full-time chair replacement. A study in Applied Ergonomics comparing an hour of typing on a ball against an office chair found more trunk movement but also 78% higher average lumbar muscle activity and more spinal shrinkage, and concluded the advantages may not outweigh the disadvantages. Short blocks alongside a proper chair are a more defensible recommendation.
What does anti-burst mean on a gym ball?
It describes how the ball fails. NHS guidance defines anti-burst material as material that deflates slowly when punctured rather than popping, and notes good quality balls are pressure-tested to support weights up to 300kg. It is a safety minimum for clinical use rather than a premium feature, and it says nothing about grip, surface durability or how long the ball will hold its shape.
Getting the order right first time
If someone typed "yoga ball", they almost certainly want the large ball, and at adult height that is the 65cm. If they described squeezing something between their knees in a Pilates class, they want the 18cm soft ball. The two are not interchangeable and the exercises do not overlap, so the name on the order is worth checking before it ships.
Beyond that, the specification checks are short. Anti-burst rated, sized to the NHS height chart, inflated to a measured diameter rather than to feel, and retired when the surface goes slick. For a clinic, that is two 65cm balls, one 55cm, and one small ball per patient place in any class you run. If you are still deciding between sizes, our guide to yoga versus Pilates is a useful companion for working out which programme the equipment is serving.
This article is intended for qualified healthcare professionals and is not a substitute for clinical training or professional judgement. Always apply evidence-based practice and refer patients to appropriate specialists where required.
