Tyre Size Reference Table – Diameter & Circumference
Look up nominal sidewall height, overall diameter, geometric circumference and wheel revolutions for selected passenger-car tyre sizes from R14 to R20.
Common tyre size dimensions table
The circumference and revolution columns are theoretical. Revolutions are rounded to the nearest whole turn; the other displayed values are rounded as labelled. “Common” means useful lookup examples, not that every size fits every vehicle.
| Tyre size | Sidewall mm | Overall diameter mm | Diameter in | Geometric circumference mm | Rev/km | Rev/mile |
|---|---|---|---|---|---|---|
| 175/65 R14 | 113.8 | 583.1 | 22.96 | 1,832 | 546 | 879 |
| 185/60 R14 | 111.0 | 577.6 | 22.74 | 1,815 | 551 | 887 |
| 185/65 R15 | 120.3 | 621.5 | 24.47 | 1,952 | 512 | 824 |
| 195/50 R15 | 97.5 | 576.0 | 22.68 | 1,810 | 553 | 889 |
| 195/55 R15 | 107.3 | 595.5 | 23.44 | 1,871 | 535 | 860 |
| 195/65 R15 | 126.8 | 634.5 | 24.98 | 1,993 | 502 | 807 |
| 205/55 R16 | 112.8 | 631.9 | 24.88 | 1,985 | 504 | 811 |
| 205/60 R16 | 123.0 | 652.4 | 25.69 | 2,050 | 488 | 785 |
| 215/55 R16 | 118.3 | 642.9 | 25.31 | 2,020 | 495 | 797 |
| 215/60 R16 | 129.0 | 664.4 | 26.16 | 2,087 | 479 | 771 |
| 225/55 R16 | 123.8 | 653.9 | 25.74 | 2,054 | 487 | 783 |
| 205/50 R17 | 102.5 | 636.8 | 25.07 | 2,001 | 500 | 804 |
| 215/50 R17 | 107.5 | 646.8 | 25.46 | 2,032 | 492 | 792 |
| 215/55 R17 | 118.3 | 668.3 | 26.31 | 2,100 | 476 | 767 |
| 225/45 R17 | 101.3 | 634.3 | 24.97 | 1,993 | 502 | 808 |
| 225/50 R17 | 112.5 | 656.8 | 25.86 | 2,063 | 485 | 780 |
| 225/55 R17 | 123.8 | 679.3 | 26.74 | 2,134 | 469 | 754 |
| 235/45 R17 | 105.8 | 643.3 | 25.33 | 2,021 | 495 | 796 |
| 225/40 R18 | 90.0 | 637.2 | 25.09 | 2,002 | 500 | 804 |
| 225/45 R18 | 101.3 | 659.7 | 25.97 | 2,073 | 483 | 777 |
| 235/40 R18 | 94.0 | 645.2 | 25.40 | 2,027 | 493 | 794 |
| 235/45 R18 | 105.8 | 668.7 | 26.33 | 2,101 | 476 | 766 |
| 245/40 R18 | 98.0 | 653.2 | 25.72 | 2,052 | 487 | 784 |
| 245/45 R18 | 110.3 | 677.7 | 26.68 | 2,129 | 470 | 756 |
| 235/35 R19 | 82.3 | 647.1 | 25.48 | 2,033 | 492 | 792 |
| 245/35 R19 | 85.8 | 654.1 | 25.75 | 2,055 | 487 | 783 |
| 255/40 R19 | 102.0 | 686.6 | 27.03 | 2,157 | 464 | 746 |
| 255/45 R19 | 114.8 | 712.1 | 28.04 | 2,237 | 447 | 719 |
| 245/35 R20 | 85.8 | 679.5 | 26.75 | 2,135 | 468 | 754 |
| 255/35 R20 | 89.3 | 686.5 | 27.03 | 2,157 | 464 | 746 |
| 275/40 R20 | 110.0 | 728.0 | 28.66 | 2,287 | 437 | 704 |
Reading example: 205/55 R16 gives a nominal 112.8 mm sidewall and 631.9 mm overall diameter. Its ideal-circle circumference is about 1,985 mm, corresponding to roughly 504 theoretical revolutions per kilometre.
Compare a custom pair, inspect a used car or learn the dynamic limits
The table contains selected geometry examples. Use the calculator for custom codes, then verify condition and approval rather than treating circumference as the whole tyre decision.
How to read 205/55 R16 91V
The dimensional code combines millimetres, a percentage and inches. The service description after it supplies information that this geometry table cannot derive.
| Marking | Meaning | Example interpretation |
|---|---|---|
| 205 | Nominal section width | 205 mm |
| 55 | Nominal aspect ratio | Sidewall height is 55% of nominal width |
| R | Construction symbol | Radial construction |
| 16 | Nominal rim diameter code | 16-inch rim diameter |
| 91 | Load index | Must be checked against an applicable load-index table and vehicle requirement |
| V | Speed category symbol | Must be checked against the vehicle, tyre specification and applicable rules |
A 55 aspect ratio does not mean a 55 mm sidewall. It means 55% of the stated width. The same profile number therefore creates different sidewall heights on 195 mm and 245 mm tyres.
Nominal tyre geometry formulas
Two sidewalls are added because the overall diameter crosses the tyre above and below the rim. Revolutions use the inverse relationship: a larger circumference needs fewer rotations to cover the same nominal distance.
Keep full precision through the formulas and round the output once. Calculating each intermediate value from an already rounded table cell can change the final revolution count.
Sidewall height by width and aspect ratio
This lookup isolates the first formula. Every value is millimetres. It helps explain why profile number alone does not describe a fixed height.
| Width | 35% | 40% | 45% | 50% | 55% | 60% | 65% |
|---|---|---|---|---|---|---|---|
| 175 mm | 61.3 | 70.0 | 78.8 | 87.5 | 96.3 | 105.0 | 113.8 |
| 195 mm | 68.3 | 78.0 | 87.8 | 97.5 | 107.3 | 117.0 | 126.8 |
| 205 mm | 71.8 | 82.0 | 92.3 | 102.5 | 112.8 | 123.0 | 133.3 |
| 225 mm | 78.8 | 90.0 | 101.3 | 112.5 | 123.8 | 135.0 | 146.3 |
| 245 mm | 85.8 | 98.0 | 110.3 | 122.5 | 134.8 | 147.0 | 159.3 |
| 255 mm | 89.3 | 102.0 | 114.8 | 127.5 | 140.3 | 153.0 | 165.8 |
For example, profile 45 produces 101.3 mm on a 225 mm tyre but 110.3 mm on a 245 mm tyre. The 45 is a ratio in both cases.
Worked calculation for 205/55 R16
- Sidewall height = 205 × 0.55 = 112.75 mm.
- Rim diameter = 16 × 25.4 = 406.4 mm.
- Overall diameter = 2 × 112.75 + 406.4 = 631.9 mm.
- Geometric circumference = π × 631.9 = approximately 1,985.17 mm.
- Revolutions per kilometre = 1,000,000 ÷ 1,985.17 = approximately 503.74.
- Revolutions per mile = 1,609,344 ÷ 1,985.17 = approximately 810.67.
The main table rounds those results for quick comparison. A manufacturer’s measured unloaded dimensions or rolling data can differ from this nominal calculation.
Geometric circumference versus rolling circumference
The formula π × diameter describes an unloaded perfect circle built exactly from the nominal code. A real tyre has tread, casing construction, manufacturing tolerances and a selected measuring rim. Two tyre models carrying the same size code do not have to measure identically in every physical detail.
Under vehicle load, the contact patch flattens and the effective rolling behaviour changes. Inflation pressure, temperature, speed, axle load and tread wear also matter. A worn tyre has less tread radius than it had when new.
Use the table for consistent preliminary geometry. Use vehicle approval documents, tyre technical data and the required measurement or test procedure when millimetres affect clearance, calibration or compliance.
How circumference change can affect indicated speed
If a vehicle remains calibrated for its original rolling size, a larger replacement circumference covers more ground per wheel revolution. Theoretical actual speed rises relative to the same displayed value. A smaller circumference produces the opposite direction.
| New-to-original circumference change | Actual at 50 displayed | Actual at 100 displayed | Actual at 130 displayed |
|---|---|---|---|
| −3% | 48.5 | 97.0 | 126.1 |
| −2% | 49.0 | 98.0 | 127.4 |
| −1% | 49.5 | 99.0 | 128.7 |
| +1% | 50.5 | 101.0 | 131.3 |
| +2% | 51.0 | 102.0 | 132.6 |
| +3% | 51.5 | 103.0 | 133.9 |
The speed unit stays the same as the displayed unit. This ratio table is not a speedometer test and does not define an allowed tyre-size tolerance. Original calibration and actual rolling circumference are separate unknowns.
Similar diameter does not prove fitment
Two codes can produce close nominal diameters while differing in width, rim diameter and sidewall. That can be useful for screening a possible plus-size combination, but it establishes only geometric similarity in one dimension.
Complete fitment also depends on rim width and offset, tyre-to-wheel compatibility, inner and outer clearance, steering lock, suspension travel, bodywork, brake clearance, fasteners, load capacity, service description and electronic-system requirements. Front and rear axles may use different approved sizes.
Never turn a small diameter percentage into universal approval. Check the exact vehicle variant, wheel and tyre combination in authoritative documents and obtain a qualified physical assessment where required.
Where to confirm an approved tyre size
- Vehicle tyre placard: selected manufacturer sizes and cold pressures for stated positions or loads.
- Owner documentation: tyre, wheel, pressure and seasonal information for the exact vehicle.
- Registration, approval papers or Certificate of Conformity: documented combinations and conditions where applicable.
- Wheel documentation: rim width, offset, load, fasteners, vehicle application and additional conditions.
- Tyre technical data: actual product dimensions, measuring rim, load and service information.
- Qualified tyre or vehicle specialist: physical clearance and full combination check.
The currently fitted code is not proof that it is original or approved. Match model, engine or powertrain, axle, variant and version rather than relying on a visually similar car.
Tyres for petrol, hybrid, electric and hydrogen cars
The geometry formula does not change with the powertrain. A 235/45 R18 code has the same nominal dimensional meaning on a petrol, diesel, hybrid, battery-electric or hydrogen vehicle.
Vehicle requirements can still differ. A heavier battery pack, axle load, torque delivery, rolling-resistance target, noise requirement or manufacturer homologation can influence the required load index, construction and approved product specification. An apparently matching size code alone does not confirm suitability.
Check the service description and vehicle documentation even when transferring between two variants that share the same body shape.
Width, rim and sidewall changes
Nominal section width does not tell you how many millimetres a new assembly moves inward or outward. Wheel width and offset determine its position, while the mounted tyre’s actual section width depends partly on the rim used for measurement and installation.
A larger rim is often paired with a lower aspect ratio to keep overall diameter similar. This is commonly called plus sizing. It can change sidewall deflection, mass, impact exposure, ride, noise and steering response, but the size code alone cannot quantify those outcomes.
The theoretical ground-clearance change equals half the diameter difference. It excludes tread wear, pressure, load, tyre deflection and suspension position.
Common tyre-table mistakes
| Mistake | Why it fails | Correction |
|---|---|---|
| Reading profile 55 as 55 mm | It is 55% of nominal width. | Multiply width by 0.55. |
| Adding one sidewall to the rim | Overall diameter crosses two sidewalls. | Add twice the sidewall height. |
| Adding inches directly to millimetres | The units are inconsistent. | Multiply rim inches by 25.4. |
| Calling nominal circumference measured rolling distance | Load, pressure, wear and construction are omitted. | Label it as geometric reference data. |
| Approving a replacement from diameter alone | Fitment, rating and legal checks are missing. | Verify the entire wheel–tyre–vehicle combination. |
Limits of the tyre size table
- Only selected passenger-car size codes are listed.
- Dimensions come from nominal width, aspect ratio and rim diameter.
- The tyre is treated as an unloaded perfect circle.
- Manufacturer tolerances, tread, wear, pressure, temperature and axle load are excluded.
- Rim width, offset, clearances, load index and speed symbol are not assessed.
- Speedometer values show only a theoretical ratio and no existing calibration margin.
- No row is a fitment, safety or legal approval.
Use the table to understand and compare nominal geometry. Use the calculator for an unlisted pair and authoritative vehicle data for any installation decision.