Introduction
Wheel offset tells you how far in or out your wheel sits from the hub mounting surface. It is measured in millimeters and comes in three types: positive, negative, and zero. Getting the right offset matters a lot. The wrong offset can cause your tires to rub against the fender or suspension parts. It can also mess up your steering and put extra stress on your wheel bearings.
This wheel offset calculator helps you compare two different wheel setups side by side. Just enter your current wheel width, offset, and tire size, then enter the new setup you want to try. The calculator will show you exactly how the new wheels and tires will sit compared to your stock setup. You can quickly see if the new combo will poke out past the fender or tuck in too far. This makes it easy to pick the right wheels and tires before you spend any money. If you also want to compare how different tire sizes affect your overall diameter and speedometer accuracy, try our Tire Size Calculator.
How to Use Our Wheel Offset Calculator
Enter your current and new wheel and tire specs to see how offset, backspacing, and fender clearance will change. You can also convert between offset and backspacing or view a handy reference chart.
Section Width (mm) — This is the width of your tire in millimeters. You can find it as the first number in your tire size (for example, 225 in 225/45R17). Enter this for both your current and new setup so the calculator can figure out how far the tire sticks out on each side.
Aspect Ratio (%) — This is the sidewall height shown as a percentage of the tire width. It is the second number in your tire size (for example, 45 in 225/45R17). This value helps the calculator find the overall tire diameter, circumference, and speedometer difference.
Rim Diameter (inches) — This is the size of your wheel measured in inches across the face. It is the last number in your tire size (for example, 17 in 225/45R17). The calculator uses this along with the sidewall height to find the full diameter of your tire and wheel combo.
Wheel Width (inches) — This is how wide your wheel is from bead seat to bead seat, measured in inches. You can usually find it stamped on the back of your wheel (for example, 7.5 in a 17×7.5 wheel). The calculator needs this to figure out backspacing and where the inner and outer edges of the wheel sit.
Wheel Offset / ET (mm) — This is the distance in millimeters from the center of the wheel to the mounting surface where it bolts to the hub. A positive number means the mounting surface is toward the outside (street side) of the wheel. A lower or negative offset pushes the wheel outward, while a higher offset tucks it inward. This is the key number that determines how your wheel sits in the fender.
Wheel Spacer (mm) — If you plan to use a spacer between the hub and the wheel, select the thickness here or choose "Custom" to type in your own value. A spacer lowers the effective offset and pushes the wheel outward. Leave this set to "None" if you are not using a spacer.
Offset ↔ Backspacing Converter — Use the second tab to quickly convert between offset and backspacing. Enter the wheel width and either the offset or the backspacing, and the calculator will instantly show you the other value in both inches and millimeters.
Reference Chart — Use the third tab to view a full table of offset-to-backspacing values for any common wheel width. Select your wheel width from the dropdown, and the table and chart will update to show backspacing along with a general note on whether each offset produces a poked, flush, or tucked stance.
What Is Wheel Offset?
Wheel offset is the distance in millimeters between the centerline of your wheel and the mounting surface where the wheel bolts to the hub. It is usually stamped on the back of a wheel as "ET" followed by a number (for example, ET45). This single number controls how far your wheel and tire sit inward or outward inside the fender. Getting it right matters for safe handling, proper clearance, and the look of your vehicle.
The Three Types of Wheel Offset
Positive offset means the mounting surface is closer to the outside (street side) of the wheel. This pushes the wheel inward toward the suspension. Most modern front-wheel-drive and all-wheel-drive cars come with positive offset wheels, typically between ET35 and ET50.
Zero offset means the mounting surface lines up exactly with the wheel's centerline. The wheel sits evenly on both sides of the hub face.
Negative offset means the mounting surface is closer to the inside (brake side) of the wheel. This pushes the wheel outward, away from the vehicle. You see negative offsets on many trucks, older muscle cars, and vehicles with deep-dish or wide-body setups.
Offset vs. Backspacing
Offset and backspacing describe related but different things. Backspacing is the distance from the back lip of the wheel to the mounting surface, measured in inches. It depends on both the wheel width and the offset. Two wheels with the same offset but different widths will have different backspacing. Our calculator converts between these two measurements instantly so you always know both values.
Why Offset Matters When Changing Wheels
When you swap to a new set of wheels or tires, the offset determines whether everything still fits. A lower offset than stock moves the wheel outward toward the fender. A higher offset tucks it inward toward the suspension and brakes. Even a 10mm change can mean the difference between a clean fit and a tire that rubs on the fender lip or hits a strut at full steering lock.
Changing the tire width at the same time makes this even more important. A wider tire on a lower-offset wheel can push the outer edge well past the fender while also pulling the inner edge closer to the suspension. That is why this calculator tracks both the inner and outer edge positions together, not just the offset number alone. You can use our Tire Size Calculator to explore how different tire dimensions affect diameter and circumference before plugging those values in here.
Effects of Incorrect Wheel Offset
- Fender rubbing — Too much poke (low offset or wide tire) causes the tire to hit the fender when you turn or go over bumps.
- Suspension contact — Too much tuck (high offset) can press the tire into the strut, coil spring, or control arm.
- Wheel bearing stress — A big offset change moves the tire's contact patch further from the bearing, creating extra leverage that wears bearings faster.
- Steering feel changes — Offset affects scrub radius. A large change can make the steering feel heavier or pull to one side under braking.
- Speedometer error — A different overall tire diameter changes how many times the tire rotates per mile, which throws off your speedometer and odometer readings.
What Are Wheel Spacers?
A wheel spacer is a flat metal disc that bolts between the hub and the wheel. It effectively lowers the offset by pushing the wheel outward. For example, adding a 15mm spacer to an ET45 wheel gives you an effective offset of ET30. Spacers are a common way to get a flush or slightly poked look without buying new wheels. This calculator lets you include spacers on both your current and new setups so you can see the true fitment difference.
Tips for Choosing the Right Offset
Stay within about 5 to 10mm of your vehicle's factory offset for the safest results. If you plan to go more aggressive, measure the gap between your current tire and the fender, and between your tire and the nearest suspension part. Those gaps tell you exactly how much room you have. Always check clearance at full steering lock and with the suspension fully compressed, not just when the car is sitting still at ride height. If you are also considering a window tint alongside your wheel upgrade, our Tint Calculator can help you find legal VLT levels for your state.
When budgeting for new wheels, keep in mind the total cost of ownership for your vehicle. Tools like our Car Depreciation Calculator can help you understand how modifications factor into your vehicle's long-term value. If you are financing the purchase, our Auto Loan Calculator can show you what the monthly payments would look like. And if you are leasing rather than buying your vehicle, check the Car Lease Calculator to make sure aftermarket wheel swaps are worth it before your lease ends.
For engine-related upgrades happening at the same time as a wheel swap, our Compression Ratio Calculator and Engine Displacement Calculator are useful companion tools. And if you want to track how your new wheel and tire combo affects fuel economy, the Gas Mileage Calculator and Fuel Cost Calculator make it easy to compare before-and-after numbers. Understanding the physics behind your drivetrain can also be helpful—our Torque Calculator and Horsepower Calculator let you explore how changes in wheel size affect the force delivered at the contact patch.