Metric tire size

275/45R21 tire size

A 275/45R21 tire is 30.7 inches (781 mm) tall and 10.8 in wide, for a 21-inch wheel, with a 4.9 in sidewall. That is the nominal size worked out from the code. Makers publish 30.5–30.8 in for real 275/45R21 tires (5 makers).

Diameter30.7 in781 mm

Width10.8 in275 mm

Sidewall4.9 in124 mm

Revs per mile656nominal, published 676–680

Wheel width8.5–10.5 inapproved by every listing

Compare 275/45R21 with other sizes

Set up for: comparing 275/45R21 with a size you're considering · Different situation?

Your current size

Current tire size

e.g. 265/70R17, 2657017 or 33x12.50R20

Where do I find my size?

It's on the tire sidewall, e.g. P265/70R17 115T, and on the tire placard sticker on the driver's door jamb (also in the owner's manual). The placard shows the size the vehicle came with; the sidewall shows what is fitted now. If they differ, use the placard as your starting point. Digits are enough here: 2657017 or 33125020.

Size you're considering

Real 275/45R21 tires: published diameters

Figures from the makers' own data books. They differ from the 30.7 in calculated figure because each tread design and construction measures slightly differently.

Maker (data book)	Published diameter	Revs per mile	Approved wheel width	Listings
BFGoodrich	30.7 in	676	8.5–10.5 in	1
Falken	30.7 in	677	8.5–10.5 in	1
Goodyear	30.8 in	680	8.5–10.5 in	1
Hankook	30.5–30.6 in	678–680	8.5–10.5 in	2
Toyo	30.7 in	676	8.5–10.5 in	1

Sources: maker data books (PDF), checked 2026-11-05. Brand names identify the data source only.

Equivalent sizes on other wheels

Sizes that appear in the maker data books with a diameter within 3% of 275/45R21. Same diameter is only one part of fitting a different size.

Wheel	Real sizes within 3% (closest first)
15-inch	265/75R15 (30.6 in, −0.3%), 31x10.50R15 (31.0 in, +0.8%), 30x9.50R15 (30.0 in, −2.4%)
16-inch	265/70R16 (30.6 in, −0.4%), 245/75R16 (30.5 in, −0.9%), 215/85R16 (30.4 in, −1.2%)
17-inch	235/75R17 (30.9 in, +0.4%), 265/65R17 (30.6 in, −0.6%), 245/70R17 (30.5 in, −0.8%)
18-inch	265/60R18 (30.5 in, −0.7%), 275/60R18 (31.0 in, +0.8%), 255/65R18 (31.1 in, +1.0%)
20-inch	275/50R20 (30.8 in, +0.3%), 295/45R20 (30.5 in, −0.9%), 255/55R20 (31.0 in, +1.0%)
22-inch	275/40R22 (30.7 in, −0.3%), 325/35R22 (31.0 in, +0.7%), 285/40R22 (31.0 in, +0.8%)

FAQ

How tall is a 275/45R21 tire?

30.7 inches (781 mm) calculated from the size code. Makers publish 30.5–30.8 in for real tires in this size; the difference comes from tread design and construction.

How do you work out the 275/45R21 diameter?

Sidewall = 275 mm × 45% = 123.8 mm. Diameter = 21 in wheel + 2 × 123.8 mm ÷ 25.4 = 30.74 in.

Is 275/45R21 a 31-inch tire?

It is about 30.7 in tall nominally, so it is close to 31 inches. Real tires in a size vary slightly by model; check the maker's spec sheet for the exact tire.

What sizes are equivalent to 275/45R21?

Real sizes within 3% of its diameter include 265/70R16 (−0.4%), 235/75R17 (+0.4%), 265/60R18 (−0.7%) and 275/50R20 (+0.3%). Equal diameter alone doesn't make a size suitable: wheel width, offset, clearance and load rating all matter.

How many revolutions per mile does a 275/45R21 make?

About 656 calculated from its unloaded diameter. Makers publish 676–680 revs per mile, measured under load (a loaded tire rolls on a slightly smaller radius), which is why published figures are higher.

Open 275/45R21 in the converter · Tire size chart · 31-inch tires

Important: These are calculated (nominal) dimensions, not a fitment recommendation. Real tires of the same size differ by brand and model (makers allow about ±3% of section height), and width changes with the rim it is mounted on. The math can't see wheel width and offset, clearance at full steering lock and suspension travel, load index, speed rating, or what your vehicle maker approves. Before changing size, check your door-jamb placard and owner's manual and ask a tire professional. A replacement tire must meet or exceed the load index and speed rating on the placard.