Tractor tyre size conversion chart – inch to metric
Tractor tyre size conversion chart: which metric sizes correspond to the old inch sizes? For example, 16.9R38 corresponds to 420/85R38 and roughly 480/70R38. All values come from the manufacturers' own dimensions in our catalogue.
Open Conversion in the app →Type any size, even just digits like 16938, and see the equivalent inch and metric sizes with diameter and percentage difference.How to read the size
16.9R38: width 16.9 in, R = radial, 38 in rim (aspect ratio about 85 %). 420/85R38: width 420 mm, height 85 % of the width, 38 in rim. A /70 or /65 is wider and lower but can have almost the same diameter.
Conversion chart: inch to metric
Bold = manufacturers' official equivalent. ≈ = close size with diameter difference. 28 inch sizes, grouped by rim.
Rim 24"
| Inch size | Metric /85 | Metric /70 | Metric /65 | Approx. diameter |
|---|---|---|---|---|
| 9.5R24 | 250/85R24 (-0.2 %) | – | – | 1 039 mm |
| 11.2R24 | 280/85R24 (-0.3 %) | 320/70R24 (+0.6 %) | – | 1 090 mm |
| 12.4R24 | 320/85R24 (+0.0 %) | 360/70R24 (+0.0 %) | ≈ 420/65R24 (+0.3 %) | 1 152 mm |
| 13.6R24 | 340/85R24 (-0.5 %) | 400/70R24 (+0.2 %) | 440/65R24 (-1.3 %) | 1 198 mm |
| 14.9R24 | 380/85R24 (+0.0 %) | 420/70R24 (-0.6 %) | 480/65R24 (-1.7 %) | 1 258 mm |
| 16.9R24 | 420/85R24 (-0.2 %) | 480/70R24 (-0.8 %) | 540/65R24 (-1.4 %) | 1 330 mm |
Rim 26"
| Inch size | Metric /85 | Metric /70 | Metric /65 | Approx. diameter |
|---|---|---|---|---|
| 16.9R26 | 420/85R26 (+0.3 %) | ≈ 480/70R26 (-0.9 %) | ≈ 540/65R26 (-0.1 %) | 1 370 mm |
Rim 28"
| Inch size | Metric /85 | Metric /70 | Metric /65 | Approx. diameter |
|---|---|---|---|---|
| 9.5R28 | 250/85R28 (+0.8 %) | – | – | 1 128 mm |
| 11.2R28 | 280/85R28 (-0.1 %) | ≈ 320/70R28 (-0.1 %) | – | 1 191 mm |
| 12.4R28 | 320/85R28 (+0.0 %) | 360/70R28 (-0.6 %) | ≈ 420/65R28 (-0.2 %) | 1 259 mm |
| 13.6R28 | 340/85R28 (-0.6 %) | 380/70R28 (+0.0 %) | ≈ 440/65R28 (-0.8 %) | 1 300 mm |
| 14.9R28 | 380/85R28 (+0.0 %) | 420/70R28 (-0.7 %) | 480/65R28 (-1.7 %) | 1 361 mm |
| 16.9R28 | 420/85R28 (+0.0 %) | 480/70R28 (-0.3 %) | 520/65R28 (-0.4 %) | 1 425 mm |
Rim 30"
| Inch size | Metric /85 | Metric /70 | Metric /65 | Approx. diameter |
|---|---|---|---|---|
| 14.9R30 | 380/85R30 (+0.0 %) | 420/70R30 (-0.5 %) | 480/65R30 (+0.3 %) | 1 416 mm |
| 16.9R30 | 420/85R30 (+0.0 %) | 480/70R30 (-0.3 %) | 540/65R30 (-0.9 %) | 1 486 mm |
| 18.4R30 | 460/85R30 (-0.1 %) | 520/70R30 (-1.3 %) | 600/65R30 (-1.3 %) | 1 556 mm |
Rim 32"
| Inch size | Metric /85 | Metric /70 | Metric /65 | Approx. diameter |
|---|---|---|---|---|
| 11.2R32 | 300/85R32 (+4.2 %) | – | – | 1 300 mm |
| 12.4R32 | 320/85R32 (+4.4 %) | – | – | 1 305 mm |
Rim 34"
| Inch size | Metric /85 | Metric /70 | Metric /65 | Approx. diameter |
|---|---|---|---|---|
| 16.9R34 | 420/85R34 (+0.0 %) | 480/70R34 (+0.1 %) | 540/65R34 (-0.6 %) | 1 589 mm |
| 18.4R34 | 460/85R34 (+0.0 %) | 520/70R34 (-0.4 %) | 600/65R34 (-0.4 %) | 1 656 mm |
Rim 38"
| Inch size | Metric /85 | Metric /70 | Metric /65 | Approx. diameter |
|---|---|---|---|---|
| 12.4R38 | 320/85R38 (+0.7 %) | – | – | 1 500 mm |
| 13.6R38 | 340/85R38 (-1.2 %) | – | – | 1 565 mm |
| 16.9R38 | 420/85R38 (+0.0 %) | 480/70R38 (+0.4 %) | 540/65R38 (-0.4 %) | 1 690 mm |
| 18.4R38 | 460/85R38 (-0.4 %) | 520/70R38 (-0.9 %) | 600/65R38 (+0.1 %) | 1 768 mm |
| 20.8R38 | 520/85R38 (-0.4 %) | 580/70R38 (-1.5 %) | 650/65R38 (-1.7 %) | 1 858 mm |
Rim 42"
| Inch size | Metric /85 | Metric /70 | Metric /65 | Approx. diameter |
|---|---|---|---|---|
| 11.2R42 | 300/85R42 (+0.7 %) | – | – | 1 565 mm |
| 18.4R42 | ≈ 460/85R42 (-0.2 %) | – | ≈ 600/65R42 (+0.2 %) | 1 844 mm |
| 20.8R42 | 520/85R42 (-0.4 %) | 620/70R42 (-0.3 %) | 710/65R42 (+0.0 %) | 1 960 mm |
Remember to calculate the front axle lead when changing size, especially on four-wheel-drive tractors. Calculate lead →
When changing tyres on a 4WD tractor, check the lead in Tire choice or Lead. Wider /70 and /65 sizes often need wider rims. Read more in Changing tractor tyre size.
Open Conversion in the appFrequently asked questions
What is 16.9R38 in metric?
According to the manufacturers' data, 16.9R38 corresponds to 420/85R38, 480/70R38, 540/65R38. The overall diameter is about 1690 mm.
What does 18.4R38 correspond to?
18.4R38 corresponds to 460/85R38, 520/70R38, 600/65R38, with an overall diameter of about 1768 mm.
Can I switch from inch to metric tyres?
Yes, if the rim fits and the overall diameter is almost the same. On four-wheel-drive tractors, check the front axle lead, especially if you change only one axle. Use the Conversion tab to compare sizes and check the lead in Tire choice.
What do /85, /70 and /65 mean?
That is the aspect ratio, the tyre height as a percentage of the width. A lower number means a wider and lower tyre. Old inch tyres have an aspect ratio of about 85.
What is 650/65R38 in inches?
650/65R38 is 20.8R38 in inches. That is the manufacturers' official equivalent. The diameter differs by about 1.8 % (about 1,826 mm vs 1,858 mm), so check the front axle lead in Lead if you mix the sizes on a four-wheel-drive tractor.
What are 600/65R38 and 650/65R42 in inches?
600/65R38 is 18.4R38 in inches (about 1,769 mm vs 1,768 mm, −0.1 %). 650/65R42 is 20.8R42 in inches, the manufacturers' official equivalent. The diameter differs by about 1.6 % (about 1,930 mm vs 1,960 mm), so check the front axle lead if you mix the sizes on a four-wheel-drive tractor.
Last updated 2026-10-15. General information. See disclaimer.