Enter a metric or flotation tire size to get overall diameter, section width, sidewall, circumference, and revolutions per mile. Free, instant, no signup.
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Type a sidewall code and get the geometry behind it: overall diameter, section width, sidewall height, and rim diameter. That is the set of numbers you need before you compare a plus-size, check fender clearance, or talk to a shop. The calculator is built for the codes printed on passenger, light-truck, and off-road tires — not a guess from a marketing photo.
Passenger metric sizes such as 275/60R20 and flotation sizes such as 35x12.50R20 both parse. You do not have to convert formats by hand before you see diameter. Aspect ratio, section width, and rim diameter are shown so you can confirm you typed the size you meant, including the difference between a metric series and a listed overall height.
Diameter alone does not tell you how a size behaves on the road. Circumference and revolutions per mile follow from the calculated diameter, which is what you need when you are thinking about speedometer error, odometer drift, or whether a taller tire will change indicated speed. Use the related comparison and speedometer tools when you are choosing between two sizes.
The formulas run locally. There is no vehicle account, no upload, and no wait for a dealer lookup. Bookmark the page and reuse it in the lot or the shop. For OEM fitment against a specific year/make/model, use Vehicle Fit; this calculator is the geometry of the size itself.
Use a metric code such as 275/60R20 or a flotation code such as 35x12.50R20. Copy it carefully — width, aspect, and rim all change the diameter.
The workspace shows overall diameter, section width, sidewall height, rim diameter, and whether the size was read as metric or flotation.
Circumference and revolutions per mile are derived from diameter. Those figures matter for speedometer error and for comparing a stock size to a replacement.
If you are stepping up a size, open the comparison, converter, or speedometer tools in this category. This page gives the geometry of one size; those tools put two sizes side by side.
Straight answers on privacy, limits, and how the workspace behaves.
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