QuickCheckTools

Tire size calculator

Enter your current tire size and a new one to compare diameter, width and sidewall height, and see how much your speedometer will change.

How to read a tire size

A size like 225/45R17 tells you three things: the tire is 225 mm wide, the sidewall is 45% as tall as it is wide (101.25 mm, or 4.0 inches), and it fits a 17-inch wheel. Overall diameter is the wheel size plus two sidewalls: here 25.0 inches.

Off-road and truck sizes like 33x12.50R15 are written in inches instead: 33 inches tall, 12.5 inches wide, on a 15-inch wheel.

Common tire sizes

SizeDiameterWidthSidewallRevs/mile
195/65R1525.0″7.7″5.0″807
205/55R1624.9″8.1″4.4″811
215/55R1726.3″8.5″4.7″767
215/60R1626.2″8.5″5.1″771
225/45R1725.0″8.9″4.0″808
225/65R1728.5″8.9″5.8″707
235/45R1826.3″9.3″4.2″766
235/65R1729.0″9.3″6.0″695
245/40R1825.7″9.6″3.9″784
245/45R1927.7″9.6″4.3″729
255/55R1829.0″10.0″5.5″694
265/70R1731.6″10.4″7.3″638
265/65R1831.6″10.4″6.8″639
275/55R2031.9″10.8″6.0″632
275/60R2033.0″10.8″6.5″611
275/65R1832.1″10.8″7.0″629
285/70R1732.7″11.2″7.9″617
285/75R1632.8″11.2″8.4″614
295/70R1834.3″11.6″8.1″589
305/55R2033.2″12.0″6.6″607
315/70R1734.4″12.4″8.7″587
33x12.50R1533.0″12.5″9.0″611
35x12.50R1735.0″12.5″9.0″576
35x12.50R2035.0″12.5″7.5″576
37x12.50R1737.0″12.5″10.0″545

Popular tire size comparisons

15-inch wheels

16-inch wheels

17-inch wheels

18-inch wheels

20-inch wheels

Questions

How do I read a tire size?

In 225/45R17, 225 is the tire width in millimetres, 45 is the sidewall height as a percentage of the width (the aspect ratio), R means radial construction, and 17 is the wheel diameter in inches. Off-road sizes such as 33x12.50R15 give the overall height (33 in), width (12.5 in) and wheel size (15 in) directly.

How much bigger can I go without problems?

A common guideline is to keep the overall diameter within about 3% of the original. Bigger changes affect speedometer accuracy, gearing, ABS and stability systems, and may rub. Always check clearance and your vehicle maker's approved sizes.

Will bigger tires change my speedometer?

Yes. Taller tires cover more ground per turn, so you travel faster than the speedometer shows. The table above shows your actual speed for each speedometer reading.

What does the speed rating or load index mean?

The number and letter after the size, such as 94W, are the load index (how much weight each tire can carry) and speed rating (the maximum safe speed). They do not affect the dimensions, so this calculator ignores them.

Are these measurements exact?

They are the design dimensions calculated from the size. Real tires vary slightly by brand and model, and a tire under load is a little shorter than its unloaded height.

What does LT mean on a tire?

LT means Light Truck. LT tires are built to carry heavier loads than P-metric (passenger) tires of the same size. The dimensions are calculated the same way.

Design dimensions calculated from the tire size. Check fitment and approved sizes with your vehicle maker or tire fitter before changing sizes.