Free tool
Tire Size Calculator
Free tire size calculator: convert metric sizes like 285/70R17 to overall diameter, width, sidewall and circumference, and compare two sizes side by side.
Metric tire sizes hide the number you actually need — the overall diameter. A 285/70R17 works out to about 32.7 inches tall, which is why it is called a "33" in lift-kit fitment guides. Enter any two sizes to compare them.
Enter two metric sizes (for example 275/65R18 and 285/70R17) and calculate.
How the maths works
Overall diameter = rim diameter + (2 × section width × aspect ratio ÷ 100) ÷ 25.4. Sidewall height is the section width multiplied by the aspect ratio percentage. Circumference is π × diameter. When you change diameter, your speedometer and effective gearing change by roughly the same percentage as the diameter.
Knowing a tire's diameter is step one. Whether it clears on your truck depends on lift height, wheel offset and trimming — check the verified data in the lift fitment checker and on your vehicle hub.