Tire Size Calculator
Compare two tire sizes, check diameter and revs per mile, and see how alternate tire sizing changes your speedometer reading.
Compare two tire sizes
Use this calculator when you are shopping alternate tire sizes, checking fitment, or trying to understand how a width or diameter change will affect your speedometer.
Tire 1
Enter width in millimeters, aspect ratio as a percentage, and wheel diameter in inches.
Example: 225 mm
Example: 50 means sidewall height is 50% of the width.
Wheel diameter in inches, such as 17 or 18.
Tire 2
Enter width in millimeters, aspect ratio as a percentage, and wheel diameter in inches.
Example: 225 mm
Example: 50 means sidewall height is 50% of the width.
Wheel diameter in inches, such as 17 or 18.
Enter two tire sizes to compare them
This page calculates overall diameter, sidewall height, circumference, revs per mile, and a 60 mph speedometer comparison so it is easier to evaluate alternate tire sizes.
Why tire size comparisons matter
Even small tire size changes can affect ride height, clearance, revs per mile, and the speed your vehicle is actually traveling when the speedometer shows a round number.
At a glance
03
quick takeaways built into this calculator section.
- 01
Width tells you how much wider a tire is in millimeters, while aspect ratio changes the sidewall height.
- 02
Overall diameter drives the speedometer difference, because a larger tire covers more ground per revolution.
- 03
Revs per mile and circumference help compare how the tire will behave beyond just the printed size label.
Tire Size Calculator
This tire size calculator compares two tire sizes and shows how an alternate setup changes overall diameter, sidewall height, circumference, revs per mile, and speedometer reading. It is built for drivers shopping for new wheels or tires, checking fitment ideas, or comparing a stock size with a wider or taller option.
The page focuses on practical comparison instead of brand shopping. You enter two tire sizes, then review the measurement differences and the speedometer effect at 60 mph.
How Tire Size Numbers Work
A size like 225/50R17 breaks into three parts: width in millimeters, aspect ratio as a percentage of width, and wheel diameter in inches.
| Part | Example | Meaning |
|---|---|---|
| Width | 225 | Tire width in millimeters |
| Aspect ratio | 50 | Sidewall height as a percentage of width |
| Wheel diameter | 17 | Wheel size in inches |
What the Calculator Compares
Sidewall height = width x aspect ratio
Overall diameter = wheel diameter + (2 x sidewall height)
Circumference = pi x diameter
Revs per mile = distance per mile / circumferenceThose values are what drive the speedometer comparison. If the second tire has a larger overall diameter, the vehicle travels farther per wheel rotation and the real speed becomes slightly higher than the indicated speed.
Why Speedometer Error Matters
Even a small change in tire diameter can alter the effective speed and mileage reading. That is why the page shows the practical statement most people care about: when the speedometer reads 60 mph, how fast are you actually traveling with the alternate tire?
Who This Tire Size Calculator Helps
This page is useful for drivers comparing discount tire size alternatives, mechanics checking fitment changes, and enthusiasts planning a wider, taller, or lower-profile setup. It is also useful when you want a quick side-by-side measurement comparison before buying.
How to Use the Tire Size Calculator
- Enter Tire 1 using width, aspect ratio, and wheel diameter.
- Enter Tire 2 with the alternate size you want to compare.
- Click Calculate.
- Review the comparison table and the speedometer statement.
Helpful Comparison Note
A wider tire does not automatically mean a taller tire. Width, aspect ratio, and wheel diameter all work together. That is why a calculator is more reliable than eyeballing the size code.
Frequently Asked Questions
How do I read a tire size?
Read it in three parts: width in millimeters, aspect ratio as a percentage, and wheel diameter in inches. For example, 225/50R17 means 225 mm wide, 50 percent aspect ratio, and a 17-inch wheel.
Will a larger tire throw off my speedometer?
Yes. A larger overall diameter usually makes the vehicle travel faster than the speedometer indicates. This page calculates that difference for you.
How much wider is a 245 tire than a 225?
It is 20 mm wider. The calculator also shows how that width change affects the rest of the tire dimensions.
Is this tire size calculator free?
Yes. It works in the browser with no login.
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