The right Pilates ball depends first on which type of ball the exercise requires. Small soft Pilates balls—often called overballs—are commonly around 18–26 cm. Large stability or fit balls are usually selected in relation to your height and how you will sit or exercise on them. They are not interchangeable, and a class instruction should take priority over a generic chart.
Size is only part of the choice. Inflation, body proportions, exercise position, surface grip and the manufacturer’s intended use can all change how a ball feels.
Small Pilates ball or large stability ball?
A small Pilates ball is a soft, lightweight prop used between the knees or ankles, behind the pelvis or upper back, under a hand, or as feedback during controlled movement. It should usually have some give.
A large stability ball—also called a fit ball, Swiss ball or exercise ball—can support more of the body. It may be used for seated work, bridging, prone exercises or supported mobility. These balls have different load ratings and safety instructions from small overballs.
Some brands also sell intermediate or mini stability balls. Always check the stated diameter and intended use rather than relying on the product name alone.
Common small Pilates ball sizes
Small soft balls are often sold around 18, 20, 23 or 26 cm. There is no single universal best size.
- 18–20 cm: lower-profile support that may feel comfortable behind the pelvis or upper back, depending on the exercise.
- 22–23 cm: a versatile middle size often used for general mat work and feedback.
- 25–26 cm: creates more height and space and may be easier for some people to hold between the knees or ankles.
These are practical tendencies, not rules. Someone with longer legs may prefer a different ball between the knees than a shorter person. A slightly deflated 26 cm ball can also sit lower than a firmly inflated 23 cm ball.
Choosing a large stability ball
Manufacturers commonly provide height-based charts for large stability balls. A typical starting pattern is approximately 55 cm for shorter adults, 65 cm for average-height adults and 75 cm for taller adults—but brand recommendations vary, and leg length, inflation and the exercise matter.
For seated work, look for a stable position in which your feet can rest securely on the floor and your hips and knees feel comfortably organised. Do not chase an exact 90-degree angle if it makes the position awkward. Check the manufacturer’s chart, maximum user weight and instructions before use.
If a teacher has designed an exercise around a particular size, follow their direction. A larger ball does not automatically make an exercise better or harder; it changes your starting height, leverage and stability.
Inflation changes the effective size
A ball’s labelled diameter usually refers to its intended inflated size. In practice, firmness changes both height and behaviour.
For many support and feedback exercises, a small Pilates ball should have enough give to mould slightly to the body. Rock-hard inflation may create excessive lift or make the prop feel unstable. Too little air can make it collapse or shift unpredictably.
Inflate gradually, test the exact position and release a little air if you cannot maintain a comfortable setup. Large stability balls should be inflated according to their own product instructions; do not deliberately exceed the stated diameter.
Match the ball to the exercise
- Behind the pelvis or upper back: choose a height and firmness that provides support without forcing the spine into an uncomfortable position.
- Between the knees or ankles: the ball should fit without pushing the legs excessively wide or encouraging a hard squeeze.
- Under a hand or foot: small changes in inflation can substantially alter stability, so begin conservatively.
- Seated on a large ball: confirm secure foot contact, appropriate ball rating and enough clear space around you.
- Home video or class: use the size specified by the instructor when possible, because the sequence may depend on that setup.
What to check before buying
Look for an exercise-grade ball with a reliable plug, clear diameter, stated load limit and care instructions. A lightly textured surface can improve grip. Studio owners may also consider cleaning compatibility, replacement plugs and whether several sizes are needed for different clients and exercises.
Do not stand on a small Pilates ball or use a large ball for an activity the manufacturer does not recommend. Inspect the surface before each session and stop using a ball that is damaged, misshapen or leaking.
Can you substitute another prop?
A folded towel or cushion may provide support in some mat exercises, but it will not create the same feedback or instability as an inflatable ball. If you are following a class, ask the instructor whether a substitution suits that movement rather than improvising under load.
The simple buying decision
First identify whether you need a small Pilates ball or a large stability ball. Then match the diameter and inflation to the exercise, your proportions and the manufacturer’s guidance. For a general small prop, a soft ball around 20–23 cm is often versatile, but it is not a universal prescription.
Continue with the Pilates equipment guide for beginners, explore Shop Pilates, or read about Pilates and Reformer sessions at Bodi Boutique.
About Jazz Collier
Jazz Collier owns and operates Bodi Boutique in Millmerran, Queensland. She holds a Certificate III in Fitness (2016), has completed Pilates training through Online Fitness Education, Studio Pilates and Core Collab, and actively teaches Pilates and fitness.
Sources and scope
Always follow the sizing, inflation and load instructions supplied with your chosen ball. For further Pilates equipment context, see Merrithew’s Pilates education library. This article provides general education and does not replace individual advice from an appropriately qualified health professional or instructor.
