Everyday Calculators
Use this tire size calculator to compare tire dimensions before planning fitment, gearing, or speedometer changes.
Live calculator
123.8 mm sidewall height.
84.02 inches circumference.
Positive means the new tire is larger than the original diameter entered.
| Part | Estimate |
|---|---|
| Sidewall height | 4.87 in |
| Overall diameter | 26.74 in |
| Circumference | 84.02 in |
Quick answer
Tire Size Calculator calculates tire diameter from section width, aspect ratio, wheel diameter and original tire diameter. The visible formula is Sidewall height = section width x aspect ratio / 100; overall diameter = wheel diameter + 2 x sidewall height.
Formula
Sidewall height = section width x aspect ratio / 100; overall diameter = wheel diameter + 2 x sidewall heightConvert sidewall height from millimeters to inches before adding it to wheel diameter in inches.
How to use
Example
Calculator use
Before relying on it
Details
These notes make the assumptions explicit, especially where the same search query can mean slightly different things.
The first number in a common tire size such as 225/55R17 is section width.
The second number is sidewall height as a percentage of section width.
Actual mounted dimensions vary by brand, load, rim width, and vehicle clearance.
Source notes
Benchmarks
The calculator is a decision aid, not a fixed rule. Use the output to compare scenarios and document your assumptions. Benchmark ranges are broad planning heuristics unless this page names a specific source for the range.
Often keeps speedometer impact small, but clearance still matters.
Check clearance, gearing, and speedometer effect.
Needs careful fitment review before purchase or installation.
Calculator accuracy
The formula, inputs, example, and limitations are shown so the result is checkable, not just a number in a box.
Sidewall height = section width x aspect ratio / 100; overall diameter = wheel diameter + 2 x sidewall height
Section width, Aspect ratio, Wheel diameter, Original tire diameter
Everyday results are quick planning checks. Unit choices, rounding, labels, measurements, local prices, and real-world constraints can change the final decision.
June 6, 2026
Toolkit Shelf. Tire Size Calculator. Last reviewed June 6, 2026. https://toolkitshelf.com/tools/tire-size-calculator
FAQ
225 is section width in millimeters, 55 is sidewall height as a percentage of width, and 17 is wheel diameter in inches.
No. It estimates tire dimensions. Verify clearance, load rating, rim width, and manufacturer guidance before changing tire size.
A different diameter changes how far the vehicle travels per wheel rotation, which can make the speedometer read high or low.
Match the result to the task type: shopping tools depend on the same unit and usable quantity, home-project tools depend on field measurements and waste, date/time tools depend on counting rules, and conversion tools depend on the unit system.
Round for readability after checking the formula and units. Keep more precision when the result feeds another calculation, and add a task-specific buffer only when shortage, waste, or timing risk matters.
Different tools may use different rounding, assumptions, default rates, methods, formulas, or input timing. Compare the visible method and inputs before relying on the output.