TIre size calculator

Use our Tire Size Calculator to quickly compare tire measurements, upgrade sizes, and fitment differences before you buy. Whether you’re looking to improve performance, get a more aggressive look, or simply replace worn tires, our tool gives you accurate specs you can trust.

Fitment Dynamics Tire Size Calculator
Enter a tire size to see its exact diameter, width, sidewall height and revs per mile.

Single Tire Size Details

Step 1: Enter your tire’s width, aspect ratio, and rim diameter.
Step 2: Review the side profile and front view.
Step 3: Use the specs below to see exact measurements.

Side Profile (Overall Diameter)

Front View (Section Width)

Current Tire Size (Baseline)

Enter the size you’re running now. This is your reference for diameter and ride-height changes.

New Tire Size (What You’re Considering)

Enter the size you’d like to upgrade or downgrade to. We’ll compare it against your current setup.

Side Profile Comparison

Front View Comparison

The first number, 275, is the tire’s section width in millimeters. The second number, 55, is the sidewall height expressed as a percentage of the tire width. The letter R indicates radial construction, and 20 is the wheel diameter in inches.

The aspect ratio determines the tire’s sidewall height. For example, a 55 aspect ratio means the sidewall height equals 55% of the tire’s section width. A higher aspect ratio usually creates a taller sidewall, while a lower ratio creates a shorter, lower-profile sidewall.

A larger overall tire diameter travels farther with each revolution, which can cause the speedometer to display a lower speed than the vehicle is actually traveling. A smaller overall diameter can cause the speedometer to display a higher speed. Use the comparison tool above to review the percentage difference between your current and proposed tire sizes.

Tire diameter is only one part of fitment. Wheel width, wheel offset, backspacing, suspension height, alignment settings, fender clearance and vehicle-specific components can all affect whether a tire rubs. The calculator helps compare dimensions, but it cannot guarantee physical clearance on every vehicle.

Yes. A larger wheel can often be paired with a lower-profile tire to maintain a similar overall diameter. A smaller wheel can usually use a tire with a taller sidewall. Keeping the overall diameter close helps reduce changes to ride height, gearing and speedometer accuracy.

Section width measures the widest point of the tire’s sidewalls when mounted on a specified wheel width. Tread width measures the portion of the tire that contacts the road. These measurements are not always identical, and actual dimensions can vary slightly by tire manufacturer and model.

Yes. The approximate ride-height change equals half of the difference in overall tire diameter. For example, moving to a tire that is two inches taller can raise the vehicle by approximately one inch, assuming there are no other suspension changes.

No. The calculator compares tire dimensions and estimated speedometer changes, but final fitment also depends on wheel specifications, suspension setup, brake clearance, body clearance and the individual vehicle. Fitment Dynamics can help verify your setup before purchasing or installing new wheels and tires.