tire size on tire sidewall

How To Find Your Tire Size — Tire Shopping 101

Have you ever called the tire store for a price and been asked your tire size? Shopping for tires online? Want bigger tires?  You’ll need to know your vehicle’s tire size. 

The best place to find the tire size is on the placard you’ll find on the driver’s side door jamb. It shows the correct original tire size and load rating and proper air pressure needed. (You can look at the sidewall of the tire too, but you’re assuming whoever put tires on last time did it correctly.)

vehicle placard with tire size shown

Besides shopping for tires, knowing your tire size gives you the dimensions you’ll need to find bigger wheels and tires too.

“Plus-sizing” tires takes the dimensions of your original tires and changes the height and width to give you the look that you want.

Whoever came up with this universal way to size tires, did a great job of confusing people with the metric, percentage, and imperial combination. 

Check out this tire size – 275/55R20 

  • 275 is the width of the tire in millimeters. 
  • 55 is the sidewall height as a percentage of the width.
  • 20 is the rim diameter in inches.

Here’s how to figure out the overall height of this 275/55R20 tire? 

  • 275mm x 55% = 151.25mm.
  • 151.25mm is the tire sidewall height. 
  • Sidewall height x 2 = 300.5mm or 11.83 inches.
  • 11.83 inches + 20 inches of rim diameter = 31.83 inches tall.

So a 275/55R20 tire is about 32 inches tall. 

Just like a pair of shoes, knowing your tire size is crucial for getting the right fit. But how would we upsize and go wider without changing the overall diameter of the tire?

Instead of a 275/55R20, take a 305/50R20 –

  • 305mm x 50% = 152.5mm.
  • 152.5 mm is the tire sidewall height. 
  • Sidewall height x 2 = 305mm or 12 inches.
  • 12 inches + 20 inches of rim diameter = 32 inches tall.

See how to get a wider tire, 305mm vs. 275mm, without changing the tire height. 

Knowing your tire size allows you to go for a wider tire while keeping the same height, so as not to affect the speedometer and sensors. It can also save you big money, because you’ll be able to shop around locally and online, comparing apples with apples. 

I’m Spencer, the owner of Kenwood Tire in West Bridgewater MA – Ask me for a personalized tire recommendation or shop online at kenwoodtire.com

And if you live further afield, you can’t go wrong with my online partner Tirebuyer. Click the banner to shop for tires and wheels, and to find an expert installer —


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