Skip to content 
Use the free wheel offset calculator below to instantly convert between offset, backspacing, and rim width — just enter any two values and get the third. Scroll down for a step-by-step guide on how to measure wheel offset by hand.
Wheel Offset Calculator
Calculate:
Offset
—
Enter any two values to get the third. Rim width & backspacing in inches, offset in millimeters.
Offset = (Backspacing − (Rim Width + 1) ÷ 2) × 25.4
Table of Contents
How to Measure Wheel Offset Manually
There are times when you’ll need to find the wheel offset manually — if the stamp is missing, or if the wheel was custom machined and the stamp no longer shows the correct offset. With this easy guide you’ll know your offset in just a few steps.
Step 1: Measure Your Backspacing
Backspacing is the distance from the mounting pad (where the wheel touches the truck/car) to the very back edge of the wheel.
- How to do it: Lay the wheel flat on the ground with the back side facing up. Place a straightedge flat across the bead seat of the wheel, then run a tape measure straight down from the bottom of the straightedge to the wheel’s mounting pad.
- Reading the measurement: In the close-up photo, the tape measure shows exactly 7 inches of backspacing.
Note: Ensure your straightedge rests on the actual rim edge, not on the tire sidewall if a tire is mounted.
Step 2: Determine Your Total Wheel Width
To calculate your offset you need the total width of your wheel.
- Fastest way: Look at the stamps on the back of the wheel — normally shown as Diameter×Width (e.g., 20×10). If the stamp isn’t there, or you have custom wheels, use the Golden Rule below.
- The Golden Rule: A wheel’s advertised rim width (e.g., a 10-inch-wide wheel) is measured from inside lip to inside lip where the tire sits. When you measure the total physical width from outside edge to outside edge, it is almost always 1 inch wider than the advertised size.
- Example: If your total physical measurement across the top is 11 inches, you actually have a 10-inch rim width.
Step 3: Calculate Your Offset
Once you have your backspacing and rim width, use the wheel offset calculator at the top of this page to find your offset instantly:
- Enter your Rim Width (in inches).
- Enter your measured Backspacing (in inches).
- The calculator shows your Offset in millimeters — or switch it to solve for backspacing or rim width.
Formula: Offset = (Backspacing − (Rim Width + 1) ÷ 2) × 25.4.
Wheel Offset Conversion Chart
Prefer to read it off a chart? Find your rim width across the top and your backspacing down the side — the intersection is your offset in millimeters. To dig deeper into wheel sizing standards, or to compare specs across builds, see our Wheel & Tire Tech Info guide.
