How much air is in a car tire?

A typical passenger car tire (225/45R17 at 32 psi) holds about 14–16 liters of internal volume. To inflate it from flat to 32 psi requires roughly 36–38 liters of free air (air at atmospheric pressure), because you're compressing about 2.2 times the tire's internal volume into it.

What is the formula for tire volume?

A tire is approximated as a torus with an elliptical cross-section. Volume = 2π² × R × a × b, where R is the distance from the center of the torus to the center of the tube (rim radius plus half the sidewall height), a is the semi-major axis of the ellipse (about 30% of section width), and b is the semi-minor axis (about 38% of sidewall height).

How do you calculate how much air a tire holds?

Measure the internal cross-section dimensions (width and height), then use the torus volume formula. Most calculators — including this one — model the cross-section as an ellipse. The result is the internal volume in liters. To find how much air compressor output is needed, multiply by the absolute pressure ratio: (gauge PSI + 14.7) ÷ 14.7.

Does tire volume change with pressure?

The physical internal volume (liters) of the tire stays essentially constant — it's fixed by the rubber and the rim. What changes with pressure is how much air mass is crammed in. At 32 psi gauge, the air inside is at about 2.2 atmospheres absolute, so the same cavity holds 2.2× as much air (by mass) as it would at atmospheric pressure.

How much air does a bicycle tire hold?

A road bike tire (700×25c at 100 psi) holds roughly 0.7–0.9 liters of internal volume. An MTB tire (29×2.3 at 25 psi) holds about 3.5–4.5 liters. The high pressure of road tires means you pump in far more air mass — about 7.8× atmospheric — even though the physical volume is smaller.

How do I calculate how much air to add to a tire?

You need the internal volume (in liters) and the pressure difference (in absolute pressure). If your tire is at 25 psi and you want 32 psi, the additional air mass required is: V × (P_target − P_current) ÷ P_atm = V × (32 − 25) ÷ 14.696 ≈ V × 0.476. For a 15-liter tire that's about 7.1 liters of free air to add.

Does a wider tire have more air volume?

Yes — significantly. A wider tire has a larger cross-sectional area, and volume scales with both width and sidewall height. A 275/55R20 holds roughly 34 liters, while a 205/55R16 holds about 12 liters — nearly a 3× difference. Wider tires also need a longer inflation time from a portable compressor.

Why does tire volume matter for TPMS and compressor sizing?

TPMS pressure drop alerts are volume-dependent: a larger tire volume changes pressure more slowly for a given leak rate, so a small nail may go unnoticed longer in a large truck tire than in a small car tire. For compressor sizing, a larger total tire volume means a longer fill time — and a flat tire on a full-size truck can require 10× the free air of a passenger car tire.

Tire Air Volume Calculator

Get the internal air volume of any tire — in liters, gallons, and cubic inches — plus how much free air you need to inflate from flat at any target pressure.

Quick Answer

A 225/45R17 tire holds approximately 14.5 liters of internal volume. To inflate it from flat to 32 psi, you need about 46 liters of free air (air at atmospheric pressure) — roughly what a standard 1-gallon portable compressor delivers in 2–3 minutes.

Tire Size

Inflation Pressure (PSI)

Common car tire sizes:

Tire Volume by Common Size

Tire Size	Volume (L)	Volume (gal)	Free Air @ 32 psi	Typical Use
195/65R15	12.1 L	3.2 gal	37 L	Economy car
205/55R16	12.4 L	3.3 gal	38 L	Compact / sedan
225/45R17	14.5 L	3.8 gal	46 L	Sport sedan
245/40R18	14.0 L	3.7 gal	44 L	Performance car
265/70R17	30.1 L	7.9 gal	93 L	Midsize truck / SUV
275/55R20	33.7 L	8.9 gal	104 L	Full-size truck
315/70R17	45.8 L	12.1 gal	141 L	Off-road truck

Formula

V = 2π² × R × a × b

Free Air = V × (P_gauge + 14.696) ÷ 14.696

V = internal volume (mm³ → convert to liters ÷ 1,000,000)
R = torus centroid radius = rim radius + sidewall height ÷ 2
a = semi-major (width) ≈ section width × 0.30
b = semi-minor (height) ≈ sidewall height × 0.38
Free Air uses Boyle's Law — P₁V₁ = P₂V₂ at constant temperature
Example: 225/45R17 → R = 268 mm, a = 67.5 mm, b = 38.5 mm → V = 2π² × 268 × 67.5 × 38.5 ≈ 13,800,000 mm³ = 13.8 L

How to Use This Calculator

1
Enter your tire size in metric format
Type the tire size as width/aspect-ratioRrim — for example, 225/45R17. Width is in millimeters; the aspect ratio is the sidewall height as a percentage of width; rim diameter is in inches.
2
Enter your target inflation pressure
Type the PSI you want to inflate to (e.g., 32 psi for a typical passenger car). The calculator uses this to show how much free air (at atmospheric pressure) is needed to reach that pressure.
3
Click Calculate Volume
The result shows total internal volume in liters, gallons, and cubic inches, plus the free air needed to inflate from zero to your target pressure.
4
Use the free-air figure for compressor planning
The free-air result (in liters or cubic feet) tells you how long it will take your portable compressor to fill a flat tire. Divide the free-air volume by your compressor's rated output in liters-per-minute to get the fill time.

Frequently Asked Questions

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