Tire size calculator
Calculate sidewall height, overall diameter, circumference, and revolutions per mile from a P-metric tire size.
What this calculator covers
Use this tire size calculator to translate a P-metric tire code into overall diameter and rolling-distance estimates.
Frequently asked questions
- How do I read a P-metric tire code?
- A code like 225/65R17 means the section width is 225 mm, the aspect ratio (sidewall height as a percentage of width) is 65, and the rim diameter is 17 inches. Enter those three numbers to get the calculated dimensions.
- What is sidewall height and how is it calculated?
- Sidewall height is the distance from the rim edge to the outer tread, calculated as width multiplied by the aspect ratio divided by 100. For a 225/65 tire that is 225 × 0.65 = 146.25 mm per sidewall.
- Why does the overall diameter matter when swapping tires?
- Overall diameter determines how far the vehicle travels per wheel revolution, which affects speedometer accuracy and clearance. Choosing a size with a noticeably different diameter from the original can cause the speedometer to read high or low.
- How is revolutions per mile calculated?
- The circumference equals π times the overall diameter. Dividing 63,360 inches per mile by the circumference gives the estimated revolutions per mile under theoretical, unloaded conditions.
Tool
Run the calculation
Result
RESULT · TIRE DIAMETER
â„–186
Primary result
28.516 in diameter
225/65R17 has a theoretical overall diameter of 28.52 in, a circumference of 89.59 in, and about 707.26 revolutions per mile.
- Tire code
- 225/65R17
- Sidewall height
- 146.25 mm (5.76 in)
- Overall diameter
- 28.52 in
- Circumference
- 89.59 in
- Revolutions per mile
- 707.26 rev/mi
Step-by-step solution
- 1.Find one sidewall height from width × aspect ratio: 225 mm × 65% = 146.25 mm.
- 2.Convert the sidewall to inches and add two sidewalls to the rim diameter for an overall diameter of 28.52 in.
- 3.Use circumference = π × diameter, then divide inches per mile by that circumference to estimate 707.26 revs/mile.
Walkthrough
Visual walkthrough
A P-metric tire size turns into diameter and rolling distance by converting the sidewall spec into inches and combining it with the rim.
01
Read the tire code
225/65R17
The width and aspect ratio define the sidewall, while the rim diameter anchors the wheel size.
02
Build the overall diameter
17 in + 2 × 5.76 in = 28.52 in
Two sidewalls wrap around one rim diameter to create the total theoretical tire diameter.
03
Translate diameter into rolling metrics
Circumference and revs per mile follow directly from the calculated diameter.
89.59 in · 707.26 rev/mi