Wheel Backspacing Calculator
Find the backspacing from width and offset. Use the calculator below. Results update as you type.
Backspacing = (Wheel Width / 2) + Offset + ~0.5" wheel lipHow the Wheel Backspacing Calculator Works
This calculator works by adding half the wheel width, a 0.5 in flange allowance and the offset in inches. Backspacing is the distance from the mounting face to the inner edge of the wheel.
- Enter the wheel width, for example 9.0 in.
- Enter the offset, for example +18 mm.
- Read the backspacing: 5.71 in (145 mm).
- Compare the backspacing with measured space to the suspension.
The Formula
The formula is Backspacing = (Wheel Width ÷ 2) + Offset + 0.5 in.
Backspacing = (Wheel Width / 2) + Offset + ~0.5" wheel lip Offset (in) = Offset (mm) ÷ 25.4Worked example: a 10.0 in wheel at −25 mm (−0.98 in) gives 5.0 − 0.98 + 0.5 = 4.52 in (115 mm).
The 0.5 in lip allowance is typical. Measure a real wheel for an exact value.
Conversion Table
The conversion table gives backspacing in inches for 5 wheel widths and 6 offsets. Values run from 3.02 in (7.0 in at ET−25) to 7.27 in (10.0 in at ET+45).
Trucks with leaf-spring or solid-axle front ends often list maximum backspacing. Pick the column that stays below that limit.
| Width (in) | ET−25 | ET−12 | ET0 | ET+18 | ET+35 | ET+45 |
|---|---|---|---|---|---|---|
| 7.0 | 3.02 | 3.53 | 4.00 | 4.71 | 5.38 | 5.77 |
| 8.0 | 3.52 | 4.03 | 4.50 | 5.21 | 5.88 | 6.27 |
| 8.5 | 3.77 | 4.28 | 4.75 | 5.46 | 6.13 | 6.52 |
| 9.0 | 4.02 | 4.53 | 5.00 | 5.71 | 6.38 | 6.77 |
| 10.0 | 4.52 | 5.03 | 5.50 | 6.21 | 6.88 | 7.27 |
Uses a 0.5 in flange allowance per side; measure a real wheel for exact values.
What Is the Wheel Backspacing Calculator?
The Wheel Backspacing Calculator is a tool that converts wheel width and offset into backspacing. Backspacing is common in the US off-road market, where wheel makers list it next to or instead of offset.
Backspacing directly measures inward reach. A wheel with too much backspacing hits the control arm, steering knuckle or leaf spring.
Common Uses
This calculator has 4 uses: off-road wheel shopping, suspension clearance, offset translation and lift-kit compliance.
- Shop off-road wheels: Compare listings given in backspacing.
- Check suspension clearance: Compare with measured inner space.
- Translate offset: Convert ET values to backspacing.
- Follow lift-kit specs: Meet the kit maker's backspacing limit.