About Tire Ruler

Tire Ruler answers the questions people ask before buying tires or lifting a truck: how big is this size, really, and what changes if I switch? Type any size and see it in inches, drawn to scale, next to the size you have now.

Tire Ruler is an independent website from the same small publisher as Supply Math (free material calculators for home and yard projects). It isn’t owned by a tire maker or retailer, and no brand pays to change the results.

What we promise

• Fast and free. No sign-up, nothing to install. The tools run in your browser, and what you type is never sent to us.
• Show the math. Every page explains the formula, so you can check it yourself.
• Honest about limits. We calculate sizes from the sidewall code. We say so, and we never claim a tire fits a specific vehicle.
• Clean ads. When the site shows ads, they’ll stay out of the way: no pop-ups, and never inside the tools.

How we calculate

• Metric sizes (e.g. 275/60R20): width = 275 mm; sidewall = width × 60%; overall diameter = wheel diameter + 2 × sidewall. 1 inch = 25.4 mm exactly.
• Flotation sizes (e.g. 33x12.50R20): diameter 33 in, width 12.5 in, wheel 20 in, as stated on the tire.
• Circumference and revolutions per mile: π × diameter; 63,360 inches per mile ÷ circumference. Real tires turn a little more per mile because they flatten under load.
• Speedometer: real speed = indicated speed × new diameter ÷ original diameter.
• Gear ratios: new ratio = old ratio × new diameter ÷ old diameter; engine RPM = mph × axle ratio × gear ratio × 336.14 ÷ tire diameter.
• Rim width ranges: a rule of thumb of about 70–88% of the section width. Each tire maker publishes the approved range for its models.
• The size list: 145 common passenger, SUV, light-truck and flotation sizes, and 160 comparisons that people commonly research (same wheel size, within 5% in height). The calculator works with any size.

Real tires of the same size can differ by a few tenths of an inch between brands and models. For fitment, load index and speed rating, check with a tire professional and your vehicle maker’s specifications.

Corrections

If a result looks wrong, tell us the page and the size: hello [at] tireruler.com. We check every report and fix confirmed errors quickly. The calculations are covered by automated tests.

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