Free Tire Size Calculator & Comparison Chart

Instantly calculate and compare tire sizes to see how changes in width, aspect ratio, or rim diameter affect your vehicle’s height, speedometer, and clearance. Our interactive tool gives you accurate fitment data for thousands of sizes—no guesswork required.

Use this calculator before upgrading your wheels or tires to confirm proper plus sizing or minus sizing. Stay within the safe ±3% overall diameter range for the best performance and ride quality.

Tire Tools

Enter Size

Enter width / aspect / rim (e.g., 275 / 55 / 20) or pick a popular size.

Side Profile (Overall Diameter)

Front View (Section Width)

Current Size

Enter your current tire’s width / aspect / rim (or pick a popular size)
Tip: Choosing a preset auto-fills both sides. Editing Current will mirror to New until you edit New.

New Size

Enter the size you’re considering to see visuals, specs, and differences.
Current New

Side Profile (Overall Diameter)

Front View (Section Width)

Keep overall diameter change within ±3% to minimize speedometer and clearance issues.

Tire Size FAQ

How do I read a tire size like 275/55R20?

275 = section width in millimeters. 55 = aspect ratio (sidewall height is 55% of width). R = radial construction. 20 = wheel diameter in inches.

What’s my overall tire diameter?

Use: Diameter = (Width × Aspect × 2 ÷ 25.4) + Rim. Example: (275 × 0.55 × 2 ÷ 25.4) + 20 ≈ 31.9". Or simply use the Tire Size Calculator above for instant results.

Will changing sizes affect my speedometer?

Yes. A larger diameter makes the speedometer read slower; a smaller diameter reads faster. Keep diameter change within ±3% to minimize errors.

What is “plus sizing” and “minus sizing”?

Plus sizing uses a larger wheel with a shorter sidewall (e.g., 18″ → 20″) to maintain overall diameter. Minus sizing does the opposite for better comfort or winter traction.

What’s the difference between LT, P, and XL tires?
  • P (Passenger): standard load, comfort focused.
  • XL (Extra Load): reinforced for higher pressure and capacity.
  • LT (Light Truck): heavy-duty, for towing or hauling with load ranges (C/D/E).
Do I need to match rim width to tire size?

Yes. Each tire size has an approved rim-width range (e.g., 275mm tires usually fit 7.5″–9.5″ rims). Staying within this range ensures proper fitment and tread wear.

Can I run staggered sizes (wider rears)?

Yes, many RWD and sports vehicles do. For AWD setups, keep overall diameters almost identical (within ~0.3″) to prevent drivetrain stress.

Metric vs. flotation sizes—what’s the difference?

Metric uses millimeters (275/55R20), while flotation uses inches (33x12.50R20). They describe the same dimensions in different systems.

What load index and speed rating should I choose?

Always match or exceed your vehicle’s factory specs. Never downgrade load index or speed rating, as it can affect safety and handling.

What tire pressure should I run after changing sizes?

Start with the OE door-jamb pressure. Adjust slightly if your load range or tire type changes to maintain correct load capacity.

All-terrain vs. mud-terrain—how do they impact fitment?

Mud-terrain tires tend to run slightly larger and may rub sooner. All-terrains are lighter and quieter—verify actual measurements before installing.

How often should I rotate tires?

Rotate every 5,000–7,500 miles. For staggered setups, rotate side-to-side only; directional tires stay on the same side unless remounted.