315/30R18 tire size
315/30R18 is a metric size: 25.4" tall, 12.4" wide, on a 18" rim — about a 25.5x12.50R18. The sidewall is 3.7" and the tire turns 793 times per mile.
315/30R18 specs
| Overall diameter (height) | 25.44" · 646 mm |
|---|---|
| Section width | 12.40" · 315 mm |
| Sidewall height | 3.72" · 95 mm (30% of width) |
| Rim diameter | 18" |
| Circumference | 79.93" · 2.030 m |
| Revolutions per mile | 793 (493 per km) |
| Inch (flotation) equivalent | 25.5x12.50R18 |
Equivalent sizes on a 18" rim
Sizes within ±5% of the overall diameter. Green rows are inside the usual ±3% limit for keeping the speedometer, ABS and gearing right; red rows are bigger changes that need clearance checks.
| Size | Diameter | Difference | Width | Speedo at 60 | |
|---|---|---|---|---|---|
| 245/40R18 common | 25.72" | +1.08% | -70 mm | 60.6 mph | compare → |
| 225/45R18 common | 25.97" | +2.09% | -90 mm | 61.3 mph | compare → |
| 225/40R18 common | 25.09" | -1.39% | -90 mm | 59.2 mph | compare → |
| 245/45R18 common | 26.68" | +4.87% | -70 mm | 62.9 mph | compare → |
| 235/45R18 common | 26.33" | +3.48% | -80 mm | 62.1 mph | compare → |
| 235/40R18 common | 25.40" | -0.15% | -80 mm | 59.9 mph | compare → |
| 255/35R18 common | 25.03" | -1.62% | -60 mm | 59.0 mph | compare → |
| 255/40R18 common | 26.03" | +2.32% | -60 mm | 61.4 mph | compare → |
| 275/35R18 common | 25.58" | +0.54% | -40 mm | 60.3 mph | compare → |
| 265/35R18 common | 25.30" | -0.54% | -50 mm | 59.7 mph | compare → |
| 275/40R18 common | 26.66" | +4.80% | -40 mm | 62.9 mph | compare → |
| 215/45R18 common | 25.62" | +0.70% | -100 mm | 60.4 mph | compare → |
| 245/35R18 common | 24.75" | -2.71% | -70 mm | 58.4 mph | compare → |
| 215/40R18 | 24.77" | -2.63% | -100 mm | 58.4 mph | compare → |
| 285/35R18 | 25.85" | +1.62% | -30 mm | 61.0 mph | compare → |
| 265/40R18 | 26.35" | +3.56% | -50 mm | 62.1 mph | compare → |
| 295/30R18 | 24.97" | -1.86% | -20 mm | 58.9 mph | compare → |
| 285/30R18 | 24.73" | -2.79% | -30 mm | 58.3 mph | compare → |
| 295/35R18 | 26.13" | +2.71% | -20 mm | 61.6 mph | compare → |
| 205/40R18 | 24.46" | -3.87% | -110 mm | 57.7 mph | compare → |
| 335/30R18 | 25.91" | +1.86% | +20 mm | 61.1 mph | compare → |
| 215/50R18 | 26.46" | +4.02% | -100 mm | 62.4 mph | compare → |
| 225/35R18 | 24.20" | -4.87% | -90 mm | 57.1 mph | calculate → |
| 305/35R18 | 26.41" | +3.79% | -10 mm | 62.3 mph | calculate → |
| 235/35R18 | 24.48" | -3.79% | -80 mm | 57.7 mph | calculate → |
| 155/60R18 | 25.32" | -0.46% | -160 mm | 59.7 mph | calculate → |
| 305/30R18 | 25.20" | -0.93% | -10 mm | 59.4 mph | calculate → |
| 145/70R18 | 25.99" | +2.17% | -170 mm | 61.3 mph | calculate → |
| 26x12.00R18 | 26.00" | +2.20% | -10 mm | 61.3 mph | calculate → |
| 26x6.00R18 | 26.00" | +2.20% | -163 mm | 61.3 mph | calculate → |
| 26x8.00R18 | 26.00" | +2.20% | -112 mm | 61.3 mph | calculate → |
| 155/70R18 | 26.54" | +4.33% | -160 mm | 62.6 mph | calculate → |
| 205/45R18 | 25.26" | -0.70% | -110 mm | 59.6 mph | calculate → |
| 345/30R18 | 26.15" | +2.79% | +30 mm | 61.7 mph | calculate → |
| 315/35R18 | 26.68" | +4.87% | 0 mm | 62.9 mph | calculate → |
Plus / minus sizing: 17" and 19" rims
Same overall height on a different rim. Check wheel width and clearance before switching.
| Size | Diameter | Difference | Width | Speedo at 60 | |
|---|---|---|---|---|---|
| 215/50R17 common | 25.46" | +0.09% | -100 mm | 60.1 mph | compare → |
| 235/45R17 common | 25.33" | -0.45% | -80 mm | 59.7 mph | compare → |
| 245/45R17 common | 25.68" | +0.94% | -70 mm | 60.6 mph | compare → |
| 235/35R19 common | 25.48" | +0.14% | -80 mm | 60.1 mph | compare → |
| 225/35R19 | 25.20" | -0.94% | -90 mm | 59.4 mph | compare → |
| 275/40R17 | 25.66" | +0.87% | -40 mm | 60.5 mph | compare → |
| 275/30R19 | 25.50" | +0.22% | -40 mm | 60.1 mph | compare → |
| 265/30R19 | 25.26" | -0.71% | -50 mm | 59.6 mph | compare → |
| 315/35R17 | 25.68" | +0.94% | 0 mm | 60.6 mph | compare → |
| 265/40R17 | 25.35" | -0.37% | -50 mm | 59.8 mph | calculate → |
| 155/70R17 | 25.54" | +0.40% | -160 mm | 60.2 mph | calculate → |
| 315/25R19 | 25.20" | -0.94% | 0 mm | 59.4 mph | calculate → |
Try another size against 315/30R18
Questions
What size is 315/30R18 in inches?
315/30R18 is about 25.4" tall and 12.4" wide on a 18-inch rim — roughly a 25.5x12.50R18 in inch sizing.
What does 315/30R18 mean?
315 mm section width, sidewall 30% of the width (3.72"), radial construction, 18-inch rim.
What tire sizes are equivalent to 315/30R18?
On the same 18" rim, within 3% of the diameter: 235/40R18 (-0.15%), 155/60R18 (-0.46%), 265/35R18 (-0.54%), 275/35R18 (+0.54%), 205/45R18 (-0.70%), 215/45R18 (+0.70%).
How many revolutions per mile does a 315/30R18 tire make?
About 793 revolutions per mile (circumference 79.9").
How these numbers are computed
Diameter = rim + 2 × sidewall, sidewall = width × aspect ÷ 100, circumference = π × diameter, revolutions per mile = 63,360 ÷ circumference. Real tires differ by brand by a few tenths of an inch. Last reviewed October 14, 2026.