Wheel Offset Calculator
Enter the width and offset of your current wheel and the new wheel (plus any spacer) to see poke, inner clearance change and backspacing for both.
A lower offset (ET) moves the wheel out, and extra width goes half outward and half inward.
Use the Wheel Offset Calculator
Building a bicycle wheel? Use the spoke length calculator and the spoke tension calculator.
Current vs New Wheel
Current / Stock Wheel
Width is stamped on the wheel (8J = 8 in). Positive ET = hub face toward the street side.
New / Aftermarket Wheel
Leave the new width blank to keep the same width. A spacer lowers the effective ET by its thickness.
Backspacing to Offset
—
ET (mm) = (backspacing − (width + 1) ÷ 2) × 25.4
Enter wheel dimensions on the left and click Calculate.
Poke (outer lip)
—
toward the fender
Inner lip
—
toward the strut / caliper
Stock Backspacing
—
inches from hub face to inner lip
New Backspacing
—
inches from hub face to inner lip
Wheel Position Change
—
Scrub Radius Impact
ET Delta
—
Scrub shift
—
Steering effect
—
Offset to Backspacing Chart (inches)
Backspacing = (width + 1) ÷ 2 + ET ÷ 25.4. Rows are wheel width, columns are offset ET in mm.
| Width | ET-25 | ET-12 | ET0 | ET+15 | ET+25 | ET+35 | ET+45 | ET+55 |
|---|---|---|---|---|---|---|---|---|
| 6 in | 2.52 | 3.03 | 3.50 | 4.09 | 4.48 | 4.88 | 5.27 | 5.67 |
| 6.5 in | 2.77 | 3.28 | 3.75 | 4.34 | 4.73 | 5.13 | 5.52 | 5.92 |
| 7 in | 3.02 | 3.53 | 4.00 | 4.59 | 4.98 | 5.38 | 5.77 | 6.17 |
| 7.5 in | 3.27 | 3.78 | 4.25 | 4.84 | 5.23 | 5.63 | 6.02 | 6.42 |
| 8 in | 3.52 | 4.03 | 4.50 | 5.09 | 5.48 | 5.88 | 6.27 | 6.67 |
| 8.5 in | 3.77 | 4.28 | 4.75 | 5.34 | 5.73 | 6.13 | 6.52 | 6.92 |
| 9 in | 4.02 | 4.53 | 5.00 | 5.59 | 5.98 | 6.38 | 6.77 | 7.17 |
| 9.5 in | 4.27 | 4.78 | 5.25 | 5.84 | 6.23 | 6.63 | 7.02 | 7.42 |
| 10 in | 4.52 | 5.03 | 5.50 | 6.09 | 6.48 | 6.88 | 7.27 | 7.67 |
| 10.5 in | 4.77 | 5.28 | 5.75 | 6.34 | 6.73 | 7.13 | 7.52 | 7.92 |
| 11 in | 5.02 | 5.53 | 6.00 | 6.59 | 6.98 | 7.38 | 7.77 | 8.17 |
| 12 in | 5.52 | 6.03 | 6.50 | 7.09 | 7.48 | 7.88 | 8.27 | 8.67 |
Quick answer
A lower offset (ET) moves the wheel out, and extra width goes half outward and half inward. Outer lip change (poke) = ½ × width change + (old ET − new ET). Inner lip change toward the strut = ½ × width change − (old ET − new ET). Work in mm (1 in = 25.4 mm). Backspacing (in) = (width + 1) ÷ 2 + ET ÷ 25.4.
Examples
| 8 in ET45 → new wheel | Poke (outer lip) | Inner lip |
|---|---|---|
| 8 in ET35 | 10.0 mm out | 10.0 mm more room |
| 9 in ET35 | 22.7 mm out | 2.7 mm closer to strut |
| 9 in ET45 | 12.7 mm out | 12.7 mm closer to strut |
| 8 in ET45 + 15 mm spacer | 15.0 mm out | 15.0 mm more room |
Enter both wheels to see poke, inner clearance, backspacing and scrub radius change.
Summary
This wheel offset calculator compares your current wheel with a new one. Enter the width and offset (ET) of each, plus an optional spacer. It shows how far the outer lip moves toward the fender (poke) and how far the inner lip moves toward the strut or caliper. It also gives the backspacing and front spacing of both wheels and the scrub radius shift. A backspacing-to-offset converter and an ET-to-backspacing chart cover common width and offset combinations.
How it works
- Enter the current (stock) wheel width in inches, as stamped on the wheel (8J = 8 in).
- Enter the current offset ET in millimeters, found on the wheel face or in your vehicle spec sheet.
- Enter the new wheel offset, and the new width if it differs (leave it blank for the same width).
- Add a spacer thickness if you plan to run one; it reduces the effective offset by the same amount.
- Click Calculate Fitment to see poke (outer lip), inner lip change, backspacing for both wheels and scrub radius shift.
- Positive poke means the outer lip sits further out toward the fender. A negative inner value means less room to the strut, spring or caliper.
Use cases
- Check how far a wider, lower-offset wheel will poke past the fender before buying.
- Confirm a new wheel will not move the inner barrel into the strut, spring perch or caliper.
- Convert backspacing to offset (or offset to backspacing) when the supplier lists only one of them.
- Work out the spacer thickness needed to make a high-offset wheel sit flush.
- Compare two aftermarket wheels side by side against the stock fitment.
- Plan a staggered fitment with different front and rear widths and offsets.
- Estimate the scrub radius change from a lower offset or a wheel spacer.
- Translate a forum fitment (e.g. 9.5 ET22) into millimeters of poke on your own car.