Free Tire Size Calculator
Paste a size. See the real dimensions — not just the numbers on the sidewall.
- 275 is the section width in millimetres, measured sidewall to sidewall.
- 60 is not millimetres: it is the sidewall as a percentage of the width. Here, 60% of 275 = 165 mm per side.
- R means radial construction. 20 is the rim diameter in inches.
- Overall diameter is the rim plus two sidewalls. That is why changing the 60 changes ride height.
What it does
Turns a tire size into overall diameter, section width, sidewall height, circumference and revolutions per mile. Accepts metric, P-metric, LT and flotation sizes.
How to use it
Type or paste the size as it is printed (275/60R20) or in flotation form (35x12.50R20). Compact digits like 2756020 also work.
How to read the result
Overall diameter is the number that changes speedometer, gearing and fender clearance. Sidewall height is what you feel in ride and pinch-flat risk. Revolutions per mile is how many times the tire turns in one mile — taller tires turn fewer times.
What this does not calculate
These are unloaded theoretical dimensions from ISO 4000-1 / TRA construction (rim diameter + two sidewalls). A loaded tire sits a little shorter. We do not model brand, load, inflation or tread wear.
Does not check whether the size fits your car, load rating, speed rating, or brake clearance.
Questions
- Is 275/60R20 the same as 32.99x10.83R20?
- Geometrically yes: 275 mm is 10.83" wide and 60-series on a 20" rim is about 33" tall. That flotation-style reading is a conversion, not a sold size.
- Why do some sites show a slightly different diameter?
- Most serious calculators use the same unloaded formula. Differences of 0.1" usually come from rounding. Loaded rolling radius is shorter than this number.
- Does the P or LT prefix change the math?
- Not the geometry. P and LT change load tables and sometimes recommended inflation, not overall diameter.
Related tools
- Tire Size Chart — Metric & InchesCommon sizes by rim diameter — metric, exact inches, and a link to run the numbers.
- Free Tire Size Comparison CalculatorThe tool people actually need: will this size change height, width and speedometer — and is it inside 3%?
- Tire Size Converter — Metric/InchesExact geometry first. Then the closest size you can actually buy — with the difference stated.
- Plus Sizing CalculatorBigger rim, shorter sidewall — without accidentally lifting or lowering the car.
- Reverse Tire Size FinderYou want about 33 inches. We list real sizes that actually sit there — not a fake 273/61R20.
Estimate — not a fitment approval.
