Metric tire size

305/30R20 tire size

A 305/30R20 tire is 27.2 inches (691 mm) tall and 12.0 in wide, for a 20-inch wheel, with a 3.6 in sidewall. That is the nominal size worked out from the code. Makers publish 27.2–27.3 in for real 305/30R20 tires (4 makers).

Diameter27.2 in691 mm

Width12.0 in305 mm

Sidewall3.6 in92 mm

Revs per mile741nominal, published 758–767

Wheel width10.5–11.5 inapproved by every listing

Compare 305/30R20 with other sizes

Set up for: comparing 305/30R20 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 305/30R20 tires: published diameters

Figures from the makers' own data books. They differ from the 27.2 in calculated figure because each tread design and construction measures slightly differently.

Maker (data book)	Published diameter	Revs per mile	Approved wheel width	Listings
Falken	27.2–27.3 in	758–760	10.5–11.5 in	2
Goodyear	27.2 in	767	10.5–11.5 in	1
Nitto	27.24 in	—	10.5–11.5 in	1
Toyo	27.2 in	763	10.5–11.5 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 305/30R20. Same diameter is only one part of fitting a different size.

Wheel	Real sizes within 3% (closest first)
15-inch	205/75R15 (27.1 in, −0.4%), 255/60R15 (27.0 in, −0.6%), 225/70R15 (27.4 in, +0.7%)
16-inch	205/70R16 (27.3 in, +0.3%), 235/60R16 (27.1 in, −0.4%), 215/65R16 (27.0 in, −0.7%)
17-inch	235/55R17 (27.2 in, −0.1%), 215/60R17 (27.2 in, −0.2%), 255/50R17 (27.0 in, −0.6%)
18-inch	235/50R18 (27.3 in, +0.2%), 295/40R18 (27.3 in, +0.3%), 215/55R18 (27.3 in, +0.4%)
20-inch	265/35R20 (27.3 in, +0.4%), 225/40R20 (27.1 in, −0.4%), 255/35R20 (27.0 in, −0.7%)
22-inch	235/30R22 (27.6 in, +1.3%), 245/30R22 (27.8 in, +2.1%), 295/25R22 (27.8 in, +2.2%)

FAQ

How tall is a 305/30R20 tire?

27.2 inches (691 mm) calculated from the size code. Makers publish 27.2–27.3 in for real tires in this size; the difference comes from tread design and construction.

How do you work out the 305/30R20 diameter?

Sidewall = 305 mm × 30% = 91.5 mm. Diameter = 20 in wheel + 2 × 91.5 mm ÷ 25.4 = 27.20 in.

Is 305/30R20 a 27-inch tire?

It is about 27.2 in tall nominally, so it is close to 27 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 305/30R20?

Real sizes within 3% of its diameter include 205/70R16 (+0.3%), 235/55R17 (−0.1%) and 235/50R18 (+0.2%). 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 305/30R20 make?

About 741 calculated from its unloaded diameter. Makers publish 758–767 revs per mile, measured under load (a loaded tire rolls on a slightly smaller radius), which is why published figures are higher.

Open 305/30R20 in the converter · Tire size chart

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.