Section width (215 in 215/65R15)
The first number in a tire size, such as 215 in P215/65R15, is the tire’s nominal section width in millimetres: its width from sidewall to sidewall.
How to read it
FMVSS 139 defines section width as the distance between the outsides of the sidewalls of an inflated tire, not counting raised lettering, decoration or protective bands; with those included, it is the overall width. NHTSA’s booklet describes the number as the width in millimetres from sidewall edge to sidewall edge, and says that in general the larger the number, the wider the tire. The figure is nominal: Yokohama says the actual tire may not match it exactly, but is close. The next number in the size, the Aspect ratio (65 in 215/65R15), is a percentage of this width.
Also searched as: first number on tire, tire width.
What each marking means under the standard that defines it. This page describes markings; it doesn’t advise on choosing, fitting, inflating or replacing tires.
How close the real width is
Australia’s design rule for passenger tyres sets a limit: a tyre’s measured section width and overall width may exceed the width specified for its size by no more than 7 percent.
Width and sidewall height
Because the aspect ratio is a percentage of the width, the sidewall’s height depends on both numbers. Carlisle’s example ST175/80D13 has a sidewall 80% of 175 mm, 140 mm tall, and Yokohama’s example at an aspect ratio of 70 is 129.5 mm. On P215/65R15, 65% of 215 mm is about 140 mm.
More tire sidewall markings
Browse symbols drawn with curves and waves or letters and numbers.
Sources
- Standard No. 139: New pneumatic radial tires for light vehicles, 49 CFR 571.139 (FMVSS 139), U.S. National Highway Traffic Safety Administration (Electronic Code of Federal Regulations), S3, definitions
- Tire Safety: Everything Rides On It, DOT HS 809 361, U.S. National Highway Traffic Safety Administration (GovInfo), Nominal Width
- Sizing Information, Yokohama Tire Corporation, Sizing Information
- How to Read Tire Markings and Sidewall Codes, Michelin North America, How to Read Tire Width and Aspect Ratio
- Vehicle Standard (Australian Design Rule 23/00 – Passenger Car Tyres) 2006, ADR 23/00, Australian Government, Federal Register of Legislation, clause 23.2.2.2.3.1
- Frequently Asked Questions, Carlisle Transportation Products (The Carlstar Group), FAQ
Last reviewed September 29, 2026 by Rory Hansen. How we research