Tire Size Calculator: Metric to Inches Conversion Chart
Convert metric tire sizes (e.g., 265/75R16) to inches. Full guide with diameter, width, sidewall height, circumference, and speedometer error chart.
Tire Size Calculator — Direct Answer
A tire size like 265/75R16 means: 265mm section width, 75% aspect ratio, R radial, 16" rim diameter. Diameter = (265 × 0.75 × 2) ÷ 25.4 + 16 = 31.6 inches. Width is 10.4 inches. Use our calculator for instant conversion.
→ Convert tire sizes with our free tire calculator
How to Read Tire Size
Every tire sidewall has the same format: Width/Aspect R Rim.
Diameter (in) = (Width × Aspect/100 × 2) ÷ 25.4 + Rim
Width (in) = Width (mm) ÷ 25.4
Circumference = Diameter × π
Where:
- Width = section width in mm
- Aspect = sidewall height as % of width
- Rim = wheel diameter in inches
- 25.4 = mm per inch
How to identify the size components
Example: P265/75R16
- P = Passenger tire (LT for light truck)
- 265 = Section width (mm)
- 75 = Aspect ratio (%)
- R = Radial construction
- 16 = Rim diameter (inches)
How to apply the formula
Example: 265/75R16
- Sidewall = 265 × 0.75 = 198.75 mm = 7.82"
- Diameter = 7.82 × 2 + 16 = 31.65"
- Width = 265 ÷ 25.4 = 10.43"
- Circumference = 31.65 × 3.14159 = 99.4"
Tire Size Conversion Chart
Common metric sizes to inches
| Metric | Diameter (in) | Width (in) | Circumference |
|---|---|---|---|
| 205/55R16 | 24.9 | 8.1 | 78.2 |
| 215/60R16 | 26.2 | 8.5 | 82.2 |
| 225/45R17 | 25.0 | 8.9 | 78.5 |
| 225/65R17 | 28.5 | 8.9 | 89.5 |
| 235/75R15 | 28.9 | 9.3 | 90.8 |
| 245/70R16 | 29.5 | 9.6 | 92.7 |
| 265/70R16 | 30.6 | 10.4 | 96.1 |
| 265/75R16 | 31.6 | 10.4 | 99.4 |
| 275/65R18 | 32.1 | 10.8 | 100.8 |
| 285/75R16 | 32.8 | 11.2 | 103.1 |
| 315/75R16 | 34.6 | 12.4 | 108.7 |
| 35x12.50R17 | 35.0 | 12.5 | 110.0 |
Tire width and rim comparison
| Metric | Inches Width | Rim Fit |
|---|---|---|
| 205 | 8.1" | 15–17" |
| 225 | 8.9" | 16–18" |
| 235 | 9.3" | 16–18" |
| 245 | 9.6" | 16–20" |
| 265 | 10.4" | 16–20" |
| 285 | 11.2" | 17–20" |
| 295 | 11.6" | 17–20" |
| 315 | 12.4" | 17–20" |
Speedometer error chart
| Size Change | Diameter Change | Speedometer Error |
|---|---|---|
| +1" diameter | +3.3% | −3.2% (reads low) |
| +2" diameter | +6.7% | −6.3% |
| −1" diameter | −3.3% | +3.4% (reads high) |
| Same diameter | 0% | 0% (accurate) |
Plus sizing: Go up 1" rim = go down 10 aspect ratio points (e.g., 225/60R16 → 225/50R17).
Common Tire Size Mistakes
Mistake 1: Confusing width and diameter
265/75R16 is not 26.5" diameter. Section width is 265mm. Diameter is 31.65".
Fix: Use the conversion formula. Don't assume.
Mistake 2: Mixing tires of different diameters
Different diameters cause transmission, ABS, and speedometer errors.
Fix: Replace all 4 tires at once, or at least both on the same axle. Match diameter within 1/4".
Mistake 3: Ignoring load range
Changing from P-metric to LT increases load capacity but stiffens ride.
Fix: Check OEM spec. Match or exceed load index for safety.
Tire Width, Diameter, and Performance
Wider tires
- Pros: More grip, better cornering
- Cons: More rolling resistance, worse MPG, more hydroplaning risk
Taller tires
- Pros: Better ground clearance, smoother ride
- Cons: Slower acceleration, wrong speedometer, worse MPG
Best practice
Stay within 3% of OEM diameter. Match width to rim capacity.
Tire Size Calculator FAQ
How do I read tire size 265/75R16?
265 = width in mm. 75 = aspect ratio (sidewall is 75% of width). R = radial. 16 = rim diameter in inches.
What does 265/75R16 equal in inches?
31.65" diameter × 10.43" width. Common 4x4 and light truck size.
How do I calculate tire diameter?
Diameter = (Width × Aspect ÷ 100 ÷ 25.4) × 2 + Rim. Example: (265 × 0.75 ÷ 25.4) × 2 + 16 = 31.65".
Can I change my tire size?
Yes, within 3% of OEM diameter. Larger changes affect speedometer, ABS, and transmission.
What does LT mean on tires?
LT = Light Truck. Higher load capacity and stiffer sidewall than P-metric. Common on trucks and SUVs.
Next Steps for Tire Selection
- Tire Size Calculator — Metric to inches
- Conversion Calculator — Units
- Fuel Cost Calculator — Trip costs
- Fuel Cost Guide — Full guide
- Auto Loan Guide — Vehicle costs
Last updated October 2026. Always verify load index and speed rating for your vehicle — incorrect tires are dangerous.