# 225/40R18 tire size in inches

- **Diameter:** 25.1 in
- **Width:** 8.9 in
- **Sidewall:** 3.54 in
- **Revs per mile:** 804

## Quick answer

A 225/40R18 tire is **25.1 inches** (637 mm) tall and **8.9 inches** (225 mm) wide, with a 3.54-inch sidewall, and fits a 18-inch wheel. In inch sizing that is roughly 25.1x8.9R18.

## 225/40R18 dimensions

| Measurement | Inches | Millimeters |
| --- | --- | --- |
| Overall diameter | 25.1 in | 637 mm |
| Section width | 8.9 in | 225 mm |
| Sidewall height | 3.54 in | 90.0 mm |
| Rim diameter | 18 in | 457 mm |
| Circumference | 78.8 in | 2002 mm |
| Revolutions per mile | 804 | -- |

## What does 225/40R18 mean?

| Part | Value | Meaning |
| --- | --- | --- |
| Width | 225 | The tire is 225 mm wide from sidewall to sidewall. |
| Aspect ratio | 40 | The sidewall is 40% as tall as the tire is wide (90.0 mm). |
| R | R | Radial construction (nearly every modern tire). |
| Rim | 18 | Fits a 18-inch wheel. |

The load index and speed rating that follow the size (for example "98H") are on the sidewall and in your door-jamb sticker. See the [load index chart](/tools/tire-load-index-chart) and [speed rating chart](/tools/tire-speed-rating-chart).

## What sizes can replace 225/40R18?

Sizes within 3% of the overall diameter, the usual limit for keeping the speedometer, ABS and stability control accurate. Check the width fits your wheel and fender, and match the load index.

| Size | Diameter | Difference | Speedometer at 60 mph |
| --- | --- | --- | --- |
| [195/65R15](/tools/tire-size/195-65r15) | 25.0 in | -0.4% | 59.7 mph actual |
| [225/45R17](/tools/tire-size/225-45r17) | 25.0 in | -0.5% | 59.7 mph actual |
| [205/55R16](/tools/tire-size/205-55r16) | 24.9 in | -0.8% | 59.5 mph actual |
| [215/55R16](/tools/tire-size/215-55r16) | 25.3 in | +0.9% | 60.5 mph actual |
| [215/45R17](/tools/tire-size/215-45r17) | 24.6 in | -1.9% | 58.9 mph actual |
| [205/60R16](/tools/tire-size/205-60r16) | 25.7 in | +2.4% | 61.4 mph actual |
| [185/65R15](/tools/tire-size/185-65r15) | 24.5 in | -2.5% | 58.5 mph actual |

## Frequently asked questions

### How tall is a 225/40R18 tire?

A 225/40R18 tire is 25.1 inches (637 mm) tall when new and correctly inflated. Real tires vary by a few tenths of an inch between brands and tread patterns.

### Can I put 225/40R18 tires on my car?

Only if your door-jamb placard or owner's manual lists 225/40R18, or a plus-size alternative within about 3% of the original diameter that clears the suspension. The wheel must be 18 inches in diameter and the right width for a 225 mm tire.

### How many revolutions per mile does a 225/40R18 tire make?

About 804 revolutions per mile, calculated from its 78.8-inch circumference. Manufacturers' published figures are usually slightly higher because a loaded tire squats a little.

## Other 18-inch sizes

- [225/55R18](https://diagxcar.com/tools/tire-size/225-55r18)
- [225/60R18](https://diagxcar.com/tools/tire-size/225-60r18)
- [235/45R18](https://diagxcar.com/tools/tire-size/235-45r18)
- [235/50R18](https://diagxcar.com/tools/tire-size/235-50r18)
- [235/55R18](https://diagxcar.com/tools/tire-size/235-55r18)
- [235/60R18](https://diagxcar.com/tools/tire-size/235-60r18)
- [245/45R18](https://diagxcar.com/tools/tire-size/245-45r18)
- [245/60R18](https://diagxcar.com/tools/tire-size/245-60r18)
- [255/55R18](https://diagxcar.com/tools/tire-size/255-55r18)
- [265/60R18](https://diagxcar.com/tools/tire-size/265-60r18)
- [265/65R18](https://diagxcar.com/tools/tire-size/265-65r18)
- [275/65R18](https://diagxcar.com/tools/tire-size/275-65r18)
- [275/70R18](https://diagxcar.com/tools/tire-size/275-70r18)

## Tire tools

- [Tire size calculator](https://diagxcar.com/tools/tire-size-calculator)
- [Tire size decoder](https://diagxcar.com/tools/tire-size-decoder)
- [Load index chart](https://diagxcar.com/tools/tire-load-index-chart)
- [Speed rating chart](https://diagxcar.com/tools/tire-speed-rating-chart)

## Tire care

- [How long do tires last?](https://diagxcar.com/how-long/tires)
- [How often to rotate tires](https://diagxcar.com/how-often/rotate-tires)
- [Uneven tire wear](https://diagxcar.com/symptoms/uneven-tire-wear)

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Source page: https://diagxcar.com/tools/tire-size/225-40r18
General information, not a substitute for a qualified mechanic.