Tire Size Calculator
Parse tire size codes (e.g. 205/55R16) and calculate sidewall height, total diameter, circumference, and revolutions per mile.
Tire Code Format
205/55R16 means: 205mm section width / 55% aspect ratio / R=radial / 16in rim diameter.
About this tool
A tire size code like 205/55R16 tells you everything about your tire's dimensions, but interpreting those numbers can be confusing. This calculator instantly decodes that cryptic notation and reveals the actual sidewall height, overall diameter, rolling circumference, and how many revolutions the tire completes per mile. Understanding these measurements matters because they affect your speedometer accuracy, fuel efficiency, and vehicle handling.
To use the tool, simply enter your tire size code in the standard format (width/aspect ratio, radial or bias, and wheel diameter) and the calculator displays all the key metrics. You'll learn your tire's sidewall height in millimeters, its total diameter in inches, how far it travels in one complete rotation, and the RPM at highway speeds. This information is invaluable for comparing tire options, diagnosing speedometer errors, or planning modifications.
Frequently Asked Questions
Code Implementation
import re
def parse_tire(code: str) -> dict | None:
m = re.match(r'^(\d{3})/(\d{2})([RDB])(\d{1,2}(?:\.\d)?)$', code.strip().upper())
if not m:
return None
width_mm = int(m.group(1))
aspect_ratio = int(m.group(2))
construction = m.group(3)
rim_inches = float(m.group(4))
sidewall_mm = width_mm * aspect_ratio / 100
total_diameter_mm = rim_inches * 25.4 + 2 * sidewall_mm
circumference_mm = total_diameter_mm * 3.14159265
revs_per_mile = 1609344 / circumference_mm
revs_per_km = 1000000 / circumference_mm
return {
"width_mm": width_mm,
"aspect_ratio": aspect_ratio,
"construction": construction,
"rim_inches": rim_inches,
"sidewall_mm": round(sidewall_mm, 1),
"total_diameter_mm": round(total_diameter_mm, 1),
"total_diameter_inches": round(total_diameter_mm / 25.4, 2),
"circumference_mm": round(circumference_mm, 1),
"revs_per_mile": round(revs_per_mile, 1),
"revs_per_km": round(revs_per_km, 1),
}
result = parse_tire("205/55R16")
for k, v in result.items():
print(f"{k}: {v}")Comments & Feedback
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