What pressure should a tennis ball have? The correct number and why it matters

The Right Pressure in a Tennis Ball - 14 PSI

An official tennis ball has an internal overpressure of approximately 14 PSI (pounds per square inch), which corresponds to about 0.97 bar or 97 kPa. This is not a random number. It is the result of decades of testing and is stipulated in the ITF (International Tennis Federation) rulebook for approved balls.

For a tennis ball to be used in official play, it must pass three tests:

All three are direct consequences of the internal pressure. Remove the pressure, and you remove the bounce. Remove the bounce, and you remove what makes tennis, tennis.

How to Measure the Pressure in a Tennis Ball at Home

Most tennis balls do not have a valve, so you cannot simply attach a regular pressure gauge. However, there are two practical methods:

Method 1: Bounce test (free, quick). Drop the ball from 254 cm height (take a tape measure and mark the point on the wall) onto a hard floor. Measure how high it bounces.

• 135-147 cm = new ball, full pressure
• 110-135 cm = approx. 70% pressure remaining, fine for recreation
• 90-110 cm = half-dead balls, club-level players will notice it
• Below 90 cm = dead ball, replace

Method 2: Pressure gauge with adapter. You can buy digital pressure gauges with a fine needle adapter (the same ones used for soccer balls) for about 200-300 DKK. Carefully insert the needle through the felt cover and rubber core, read the pressure, and the ball will seal itself after measurement. The loss during measurement is minimal.

The bounce test is quicker and requires no equipment. For 9 out of 10 tennis players, it is sufficient to assess whether a ball is worth playing with.

Why Does Pressure Drop - And How Quickly?

The rubber core of a tennis ball is not 100% airtight. It is porous at a molecular level, and air molecules slowly diffuse through the material. This is pure physics and cannot be stopped - only slowed down.

Two factors control how quickly this happens:

1. Pressure gradient. The greater the difference between the pressure inside the ball and outside, the faster it leaks. A new ball at 14 PSI leaks faster than a half-empty one at 9 PSI. This is why the pressure drop is fastest in the first few weeks and slower later on.

2. Mechanical stress. When the ball hits a racket or the court, the rubber core deforms. The microscopic movements in the rubber matrix briefly open small channels where air can escape more quickly. Play significantly accelerates the pressure drop.

Practical consequence: an unused ball loses about half its pressure in 8 weeks. A played ball does so in 2-3 weeks. This explains why you can open a "new" tube of tennis balls you've had stored for 4 months and find that it feels terrible to play with - the ball has almost no pop left.

What do you feel as a player when the pressure is incorrect?

This is not theory. It's something every club tennis player has felt - even if they haven't put it into words.

At 14 PSI (new ball): Clear pop on every strike. The ball takes spin precisely. The racket arm doesn't need to work hard to get depth. The serve flies. The smash ball returns quickly to the court.

At 11 PSI (after ~3 weeks): Still fine for recreational play. Slightly softer first touch. Advanced players notice it in volley timing.

At 9 PSI (after ~6 weeks): Clearly softer bounce. You work more with your arm. Topspin baseline play becomes heavy. The ball flies shorter with the same power. Less control.

At 7 PSI (after ~8 weeks): The ball feels "dead". It bounces tiredly. You make damaging compensatory swings because there's no pop to rely on. The elbow and shoulder work more - a known path to tennis elbow with prolonged play with dead balls.

The last point is worth pausing at: playing with consistently low-pressure balls is an underestimated factor in overuse injuries. You unconsciously compensate with greater arm strength, which over time puts more strain on tendons and joints than necessary.

How to Maintain the Pressure in Your Tennis Balls

The only effective method is pressure storage. The principle is simple: if the pressure outside the ball matches the pressure inside, the gas has no direction to diffuse in. The pressure drop almost completely stops.

Pressurebox Pro is designed precisely for this. You place the balls in the container after play, and an internal compressor maintains approximately 14 PSI around them - it preserves the pressure a fresh tennis ball needs. The balls remain in the same environment as they were packaged in at the factory.

Things that help to a lesser extent:

• Keep the tube lid airtight - reduces diffusion by approx. 30-40%
• Store at 18-22 degrees Celsius - heat accelerates diffusion
• Avoid direct sunlight - UV degrades the felt cover
• Keep away from moisture - the felt absorbs water and changes play feel

But none of them stop diffusion. They slow it down. The difference is roughly like the difference between a leaky bucket with tape over the hole and a bucket that doesn't have a hole. The first still leaks - just slower.

If you want to delve deeper into the topic, read our test of 5 tennis ball brands over 12 weeks or the corresponding guide to padel ball lifespan.

If you want to measure the pressure in a ball yourself, we have a step-by-step home measurement guide based on the ITF deformation principle. The bounce requirement and the difference between ITF and FIP are explained in the article on tennis ball bounce height, and winter storage particularly affects pressure. The difference between felt types is described in the guide on regular-duty vs extra-duty tennis balls.