Tire Size Comparison Calculator
Put two tire sizes side by side. See every change. Use the calculator below. Results update as you type.
How the Tire Size Comparison Calculator Works
This calculator works by computing every dimension for 2 tire sizes and showing the difference in units and percent. It answers one question: how different is the new tire from the old one?
- Enter Tire 1, the current size, for example 265/70R17.
- Enter Tire 2, the size you are considering, for example 285/70R17.
- Read the diameter change: +3.49% (+1.10 in, +28 mm).
- Read width, sidewall, circumference, revs per mile and speedometer changes in the same panel.
The tool flags any diameter change outside ±3%. The 285/70R17 example fails that check by 0.49 points.
The Formula
The formula is Difference (%) = (Tire 2 Value − Tire 1 Value) ÷ Tire 1 Value × 100. It runs on each dimension.
Diameter Change (%) = (D2 − D1) ÷ D1 × 100 Width Change (mm) = W2 − W1 Sidewall Change (mm) = (W2 × AR2 − W1 × AR1) ÷ 100 True Speed = Indicated Speed × D2 ÷ D1Worked example for 205/55R16 to 225/45R17: D1 = 24.88 in, D2 = 24.97 in, change = +0.38%. A speedometer showing 60 mph now means 60.2 mph.
Conversion Table
The conversion table compares 10 popular size swaps by diameter. Changes range from +0.38% (a classic Plus-1 swap) to +8.72% (265/70R17 to 315/70R17).
Six of the 10 swaps fall inside ±3%. The 4 swaps above 3% are all truck and SUV upsizes, where owners trade speedometer accuracy for height.
| Tire 1 | Tire 2 | Tire 1 Dia (in) | Tire 2 Dia (in) | Change |
|---|---|---|---|---|
| 205/55R16 | 225/45R17 | 24.88 | 24.97 | +0.38% |
| 205/55R16 | 215/55R16 | 24.88 | 25.31 | +1.74% |
| 225/45R17 | 235/40R18 | 24.97 | 25.40 | +1.72% |
| 215/60R16 | 225/55R17 | 26.16 | 26.74 | +2.24% |
| 225/65R17 | 235/65R17 | 28.52 | 29.03 | +1.79% |
| 235/65R17 | 245/65R17 | 29.03 | 29.54 | +1.76% |
| 265/70R17 | 285/70R17 | 31.61 | 32.71 | +3.49% |
| 265/70R17 | 315/70R17 | 31.61 | 34.36 | +8.72% |
| 245/75R16 | 265/75R16 | 30.47 | 31.65 | +3.88% |
| 275/55R20 | 275/60R20 | 31.91 | 32.99 | +3.39% |
What Is the Tire Size Comparison Calculator?
The Tire Size Comparison Calculator is a tool that compares 2 tire sizes across diameter, width, sidewall, circumference, revolutions and speedometer effect. It is the most used tool for anyone changing tire sizes.
Tire 1 is the baseline, usually the factory size from the door placard. Tire 2 is the candidate. Every difference is reported as Tire 2 minus Tire 1, so a positive number means the new tire is larger.
Common Uses
This calculator has 5 uses: upgrade checks, winter setups, lift planning, replacement shopping and speedometer prediction.
- Check upgrades: Confirm a wider or taller size stays within ±3%.
- Plan winter setups: Compare a narrower winter size with the summer size.
- Plan lifts: See how much height a larger tire adds.
- Shop replacements: Compare in-stock sizes with the factory size.
- Predict speedometer error: Read true speed at any indicated speed.