Flotation-to-Metric Tire Converter
Convert flotation tire sizes like 33x12.50R17 into the closest metric equivalent. See exact aspect ratio and diameter error for each match.
Find approximate metric size equivalents.
Flotation-to-Metric Tire Converter: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Flotation-to-Metric Tire Converter Works?
The Flotation-to-Metric Tire Converter works by converting the flotation width to millimeters, solving for the aspect ratio that matches the flotation diameter, and rounding to the nearest standard metric size. The process has 4 steps.
Enter the flotation size
Type a size such as 35x12.50R17.
Convert the width
The converter turns 12.5 in into 317.5 mm and picks the nearest standard width, 315 mm.
Solve the aspect ratio
The converter divides the 9 in (228.6 mm) sidewall by 315 mm for an exact aspect ratio of 72.6%.
Round and check
The converter rounds to 315/75 R17 and reports the metric size's diameter and its gap from 35 in.
Flotation-to-Metric Tire Converter Formula
The Flotation-to-Metric Tire Converter formula is AR = ((D − Rim) × 25.4 ÷ 2) ÷ W_mm × 100.
W_mm = W_in × 25.4 → nearest 5 mm endingAR = (D − Rim) × 12.7 ÷ W_mm × 100AR_std = round(AR ÷ 5) × 5- D
- Flotation diameter (in)
- W_in
- Flotation width (in)
- W_mm
- Nearest standard metric width (mm)
Worked example
A 33x12.50R17 tire has a 317.5 mm width and an 8 in (203.2 mm) sidewall. With a 315 mm metric width, the exact aspect ratio is 203.2 ÷ 315 × 100 = 64.5%, so the closest metric size is 315/65 R17 at 33.12 in (+0.37%).
Flotation-to-Metric Tire Converter Conversion Table
The Flotation-to-Metric Tire Converter conversion table lists the closest metric size for 8 common flotation sizes and the diameter gap of each match.
| Flotation size | Nearest width | Exact aspect ratio | Closest metric size | Metric diameter (gap) |
|---|---|---|---|---|
| 31x10.50R15 | 265 mm | 76.7% | 265/75 R15 | 30.65 in (-1.13%) |
| 33x12.50R15 | 315 mm | 72.6% | 315/75 R15 | 33.60 in (+1.83%) |
| 33x12.50R17 | 315 mm | 64.5% | 315/65 R17 | 33.12 in (+0.37%) |
| 33x12.50R18 | 315 mm | 60.5% | 315/60 R18 | 32.88 in (-0.36%) |
| 35x12.50R17 | 315 mm | 72.6% | 315/75 R17 | 35.60 in (+1.72%) |
| 35x12.50R20 | 315 mm | 60.5% | 315/60 R20 | 34.88 in (-0.34%) |
| 37x12.50R17 | 315 mm | 80.6% | 315/80 R17 | 36.84 in (-0.43%) |
| 37x13.50R20 | 345 mm | 62.6% | 345/65 R20 | 37.66 in (+1.78%) |
What is Flotation-to-Metric Tire Converter?
A Flotation-to-Metric Tire Converter is a tool that finds the metric tire size nearest to an inch-based flotation size. Metric sizes come in 10 mm width steps and 5-point aspect ratio steps, so an exact match rarely exists.
The converter shows the diameter gap of each metric match, so a buyer knows the metric tire is slightly taller or shorter than the flotation tire.
Metric light truck sizes often cost less and come in more tread patterns than flotation sizes.
What are the uses of Flotation-to-Metric Tire Converter?
There are 4 main uses of the Flotation-to-Metric Tire Converter, including wider shopping and spare matching.
Wider shopping
Find metric sizes that match a flotation size for more brand choice.
Spare matching
Match a metric spare to flotation road tires.
Load comparison
Compare metric LT load ranges with the flotation tire's rating.
Imported vehicle sizing
Find metric sizes for vehicles sold in markets without flotation sizes.
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