Tire Size Conversion
235/45r18 to inches
235/45R18 has a nominal width of 235 mm and an estimated outside diameter of 26.33 inches. Actual tire dimensions vary by manufacturer and operating conditions.
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NIST describes the standard inch as exactly equivalent to 25.4 mm
. NIST length definition. Michelin — reading tire markings. Method and limitations.
Nominal tire-size calculations for 235/45r18: section width, estimated sidewall height, outside diameter, circumference, and revolutions per mile. Actual dimensions vary by tire, rim, pressure, load, and wear.
Section width
235 mm
9.25 inches
Sidewall height
105.8 mm
4.16" (45% of width)
Wheel (rim) diameter
18"
457.2 mm
Overall diameter
26.33"
668.7 mm
Estimated circumference
82.71"
2100.8 mm
Estimated revolutions per mile/km
766 revs/mile
476 revs/km
About 235/45r18 tire size
The size 235/45r18 indicates a section width of 235 mm (9.25 inches), an aspect ratio of 45% (sidewall height 105.8 mm or 4.16 inches), and a 18-inch wheel. Estimated outside diameter calculates to 26.33 inches (668.7 mm), with an estimated geometric circumference of 82.71 inches.
Use these measurements to estimate speedometer error and clearance changes when switching sizes. For multi-size comparison and speed error calculation, try our dedicated tire size calculator.
Common tire sizes
Compare the nominal dimensions of 235/45r18 with other tire sizes. Confirm vehicle approval, rim compatibility, clearances, and load and speed ratings separately.
Sources and calculation notes
235/45R18 has a nominal width of 235 mm and an estimated outside diameter of 26.33 inches. Actual tire dimensions vary by manufacturer and operating conditions.
Method: Sidewall height in mm = width × aspect ratio / 100. Estimated diameter in mm = rim inches × 25.4 + 2 × sidewall height; circumference = π × diameter.
Scope: Actual inflated size and rolling circumference vary by product, load, pressure and wear. Fitment also requires clearance, rim width, load and speed checks.
Content maintained by mmtoinches.im. Updated and reference notes reviewed . How we calculate and present measurements. Sources support the stated definitions; examples and calculators are not certification of a product or compliance with a standard.