Tire size calculator: how does another size compare?
Type each size the way the sidewall shows it. Free, no sign-up, nothing leaves your browser.
Copy the size from the sidewall, letters in front included: 225/65R17 102H. Add the load index and speed rating after it if you can see them. Spaces and capitals don't matter.
Fix one part of the size without retyping it. The plus and minus buttons step through the values this calculator supports, so you can watch the comparison move.
Optional. Type a second size, like a winter set, to see how much taller or shorter, wider and longer around it is, what your speedometer would show, and how its ratings compare.
Fix one part of the size without retyping it. The plus and minus buttons step through the values this calculator supports, so you can watch the comparison move.
On the driver's door edge or door pillar, under "Tire and Loading Information" or "Renseignements sur les pneus et le chargement". Copy the size after "Original tire size" or "Size".
Fix one part of the size without retyping it. The plus and minus buttons step through the values this calculator supports, so you can watch the comparison move.
The last four digits of the tire identification number, often right after DOT: week, then year. 4421 is week 44 of 2021. The full number may be on one side of the tire only.
The last four digits of the tire identification number, often right after DOT: week, then year. 4421 is week 44 of 2021. The full number may be on one side of the tire only.
Your tire size, read back
Example sizes. Type yours over them.
This comparison is on hold.
Type the size from your sidewall to see it in plain words.
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Questions for your installer
Want a shop to check these? Find tire stores and wheel alignment shops near you.
Inflate to the pressure on your door placard. The pressure moulded on the sidewall, in kPa, is the tire's maximum, not the one to use.
Nominal sizes, worked out from the markings alone. A shop that can see your car and the tire can tell you what this page can't.
Nothing you type leaves your browser or is saved. Print and Copy are the only ways to keep it.
Tire size chart: reading 225/65R17 102H part by part
Here's 225/65R17 102H taken apart, in the order the sidewall shows it.
225/65R17102H
| Part | What it means |
|---|---|
| (none) | No letter in front: metric passenger tire. P: P-metric passenger. LT: light truck. |
| 225 | Section width in millimetres, sidewall to sidewall. |
| 65 | Aspect ratio: sidewall height as a percentage of the width. |
| R | Radial construction. ZR: radial built for more than 240 km/h. |
| 17 | Wheel diameter in inches. |
| 102 | Load index. Look it up in the load index chart: 102 is 850 kg. |
| H | Speed rating. Look it up in the speed rating chart: H is 210 km/h. |
Light truck sizes read the same way: LT245/75R16 120/116S carries two load indexes, one for single and one for dual mounting.
Flotation sizes are in inches: 31x10.50R15 is about 31 inches tall and 10.50 inches wide, on a 15-inch wheel, or 787.4 mm tall.
Tire speed rating chart in km/h
The letter after the load index is the speed rating: the top speed the tire is rated for, in km/h.
| Speed rating | Top speed, km/h | mph | Yours |
|---|---|---|---|
| L | 120 | 75 | |
| M | 130 | 81 | |
| N | 140 | 87 | |
| P | 150 | 93 | |
| Q | 160 | 99 | |
| R | 170 | 106 | |
| S | 180 | 112 | |
| T | 190 | 118 | Considering |
| U | 200 | 124 | |
| H | 210 | 130 | Now |
| V | 240 | 149 | |
| W | 270 | 168 | |
| Y | 300 | 186 | |
| (Y) | above 300 | above 186 |
The letters run in speed order, not alphabetical order: H sits between U and V.
ZR in the size means more than 240 km/h. A rating in brackets, like (96Y), means more than 300 km/h; the tire maker has the figure.
Source: U.S. Tire Manufacturers Association, Tire Care and Safety guide (speed symbols table) and Tire Information Service Bulletin Vol. 58 No. 1 (L); km/h as in UN Regulation No. 30. Last checked October 8, 2026.
Tire load index chart in kg
The number before the speed rating is the load index: what one tire is rated to carry, in kilograms.
| Load index | kg per tire | lb | Yours |
|---|---|---|---|
| 60 | 250 | 551 | |
| 61 | 257 | 567 | |
| 62 | 265 | 584 | |
| 63 | 272 | 600 | |
| 64 | 280 | 617 | |
| 65 | 290 | 639 | |
| 66 | 300 | 661 | |
| 67 | 307 | 677 | |
| 68 | 315 | 694 | |
| 69 | 325 | 717 | |
| 70 | 335 | 739 | |
| 71 | 345 | 761 | |
| 72 | 355 | 783 | |
| 73 | 365 | 805 | |
| 74 | 375 | 827 | |
| 75 | 387 | 853 | |
| 76 | 400 | 882 | |
| 77 | 412 | 908 | |
| 78 | 425 | 937 | |
| 79 | 437 | 963 | |
| 80 | 450 | 992 | |
| 81 | 462 | 1,019 | |
| 82 | 475 | 1,047 | |
| 83 | 487 | 1,074 |
| Load index | kg per tire | lb | Yours |
|---|---|---|---|
| 84 | 500 | 1,102 | |
| 85 | 515 | 1,135 | |
| 86 | 530 | 1,168 | |
| 87 | 545 | 1,202 | |
| 88 | 560 | 1,235 | |
| 89 | 580 | 1,279 | |
| 90 | 600 | 1,323 | |
| 91 | 615 | 1,356 | |
| 92 | 630 | 1,389 | |
| 93 | 650 | 1,433 | |
| 94 | 670 | 1,477 | |
| 95 | 690 | 1,521 | |
| 96 | 710 | 1,565 | |
| 97 | 730 | 1,609 | |
| 98 | 750 | 1,653 | |
| 99 | 775 | 1,709 | |
| 100 | 800 | 1,764 | Considering |
| 101 | 825 | 1,819 | |
| 102 | 850 | 1,874 | Now |
| 103 | 875 | 1,929 | |
| 104 | 900 | 1,984 | |
| 105 | 925 | 2,039 | |
| 106 | 950 | 2,094 | |
| 107 | 975 | 2,150 |
| Load index | kg per tire | lb | Yours |
|---|---|---|---|
| 108 | 1,000 | 2,205 | |
| 109 | 1,030 | 2,271 | |
| 110 | 1,060 | 2,337 | |
| 111 | 1,090 | 2,403 | |
| 112 | 1,120 | 2,469 | |
| 113 | 1,150 | 2,535 | |
| 114 | 1,180 | 2,601 | |
| 115 | 1,215 | 2,679 | |
| 116 | 1,250 | 2,756 | |
| 117 | 1,285 | 2,833 | |
| 118 | 1,320 | 2,910 | |
| 119 | 1,360 | 2,998 | |
| 120 | 1,400 | 3,086 | |
| 121 | 1,450 | 3,197 | |
| 122 | 1,500 | 3,307 | |
| 123 | 1,550 | 3,417 | |
| 124 | 1,600 | 3,527 | |
| 125 | 1,650 | 3,638 | |
| 126 | 1,700 | 3,748 | |
| 127 | 1,750 | 3,858 | |
| 128 | 1,800 | 3,968 | |
| 129 | 1,850 | 4,079 | |
| 130 | 1,900 | 4,189 |
That's the tire's rated load, not what it carries at every pressure. Use your door placard pressure and ask your installer about load capacity at that pressure.
For V, W and Y tires, UN Regulation No. 30 lowers the allowed load on cars built to go faster than 210, 240 and 270 km/h.
Source: UN Regulations No. 30 (indexes to 120) and No. 54 (121 to 130), Annex IV, as published in the EU Official Journal in 2008. Pounds: our conversion, rounded to the nearest pound. Last checked October 8, 2026.
Winter tires: what the markings mean in Quebec, B.C. and Ontario
You've typed M+S, or you're looking at a used set and wondering whether it counts. There's no single Canadian answer. The federal tire rules define a winter tire one way, and each province that regulates them writes its own rule. Here's what the federal rules and three provinces say on their own pages, with the date each page carries.
| Where | What its page says | Its date |
|---|---|---|
| Canada, federal tire rules | A winter tire has to pass a snow traction test against a reference tire and carry the Alpine symbol on at least one sidewall: three peaks, the middle one tallest, with a six-sided snowflake inside. The letters M and S play no part in the definition. | Motor Vehicle Tire Safety Regulations, current to September 21, 2026 |
| Canada, Transport Canada's advice | Install winter tires in sets of four. Handling improves when all four share the same type, size, speed rating and load index. Don't mix tread patterns, construction or sizes, and don't drive on snow with less than 4 mm of tread. | Transport Canada, modified October 6, 2025 |
| Quebec | From December 1 to March 15, vehicles registered in Quebec, rentals included, need winter tires. A tire complies if it carries the winter pictogram or is studded. Trailers and vehicles registered outside Quebec are among the exceptions. | quebec.ca, updated October 5, 2026 |
| British Columbia | On highways signed for winter tires, a winter tire needs at least 3.5 mm of tread. It must meet the federal snow-traction test or the RMA's M/S specifications, and the maker must mark it with the three-peaked mountain and snowflake symbol or the letters M and S. Most signed routes run October 1 to April 30; some end March 31. The province recommends the snowflake symbol and warns against mixing sizes. | B.C. regulation current to October 6, 2026; routes page updated November 24, 2025 |
| Ontario | Its page sets no winter tire requirement. It recommends four winter tires, never mixed with other types, points to the three-peak mountain snowflake symbol as the easiest sign, and says you could get an insurance discount: ask your insurer. | ontario.ca, updated December 29, 2022 |
| Other provinces | Alberta, Saskatchewan, Manitoba, New Brunswick, Nova Scotia, Prince Edward Island, and Newfoundland and Labrador aren't covered on this page. |
These are government summaries. The linked regulations set the legal requirements.
Quebec's regulation itself, in the version current to October 24, 2025, adds two details. It also applies to anyone renting out a vehicle in Quebec, wherever that vehicle is registered. And it counts a studded tire only when the studs are used the way Quebec's studded-tire regulation allows. For changes since then, check the Quebec government page.
Winter rules last checked October 8, 2026.
How the tire size calculator works
It reads the size you typed.
We read it the way a tire shop would: the letters in front, the width in millimetres, the aspect ratio, R for radial, the wheel size in inches, then the load index and speed rating. LT sizes and flotation sizes like 31x10.50R15 read too. If a part doesn't add up, we tell you which one and stop rather than guess.
It works out the height, in millimetres.
The sidewall is the width times the aspect ratio: on a 225/65R17 that's 225 x 0.65 = 146.25 mm. The whole tire is the wheel plus two sidewalls, 17 x 25.4 + 2 x 146.25 = 724.3 mm, or 28.52 inches. UN Regulation No. 30 uses the same formula for a tire's design diameter.
It compares like with like.
We work every difference out from the unrounded millimetres and round it once, at the end. Set a 215/70R16 winter tire against that 225/65R17 and it comes out 16.9 mm shorter, 2.3% smaller overall. If a difference is too small to show, you'll see less than 0.1%, never a zero.
It works out your speedometer.
The speedometer counts how fast the wheels turn. A shorter tire covers less road per turn, so the gauge reads high: at an indicated 100 km/h on that winter set you'd be doing about 97.7. We assume the gauge reads true on the size you compare against, and we name that size every time. Give us your placard size and that's the one we use.
It looks up the codes.
We look the load index and speed rating up in the two dated charts on this page, in kilograms and km/h. A code they don't cover stays exactly as you typed it, with a question for your installer. We never swap in the nearest value.
It stops short of a verdict.
Nominal isn't measured. The cited 2008 UN rule for approving car tires lets a new radial tire's diameter come out from 3% under to 4% over its nominal sidewall height on each side; for a 225/65R17 that's roughly 715.5 to 736.0 mm. Makers publish measured dimensions for each model, and those beat any calculator. So you get numbers and questions here, and no green tick.
Who this is for
You've got two tire sizes and one car. Say it's October, the changeover is coming, and the winter set you found sits on smaller wheels. Or the shop is out of your size and offers the next one over. Or you just want to know what 102H on your sidewall means in kilograms and km/h. Pickup owners weighing an LT size against a 31-inch flotation tire can put both in. We do the arithmetic and hand you the questions. The person mounting the tires answers them.
Canadian driver questions about tire sizes
Can my winter tires be a different size?
Nothing on this page can settle that for your car. Transport Canada's advice is that new tires match the originals in size, load capacity and speed rating. It also says handling improves when all four winter tires share the same type, size, speed rating and load index. If your winter set is a different size, type both sizes in. The overall diameter shows what changes for the speedometer, and the questions show what to ask your installer.
Is M+S a winter tire?
It depends on where you drive. Quebec counts only tires with the winter pictogram, or studs. B.C. accepts M/S on signed winter routes with at least 3.5 mm of tread, provided the tire meets the RMA specifications or the federal snow-traction test. The maker must mark M/S or the three-peak symbol. Federal winter tires pass the snow test and carry the three-peak symbol. The calculator reads M+S back to you and changes no number.
What does the three-peak mountain and snowflake symbol mean?
It's the Alpine symbol in the federal tire standard: three peaks, the middle one tallest, with a six-sided snowflake inside. Under the federal rules, a tire counts as a winter tire only if it carries the symbol and beats a reference tire by a set margin in a snow traction test. Transport Canada says tires carrying it are designed for severe snow. Ontario's page calls it the easiest way to spot a winter tire.
Why is my winter tire's speed rating lower?
Check the letter after the load index. T is rated for 190 km/h and H for 210, so a T winter set against an H on the placard is a step down. Transport Canada's advice is that new tires carry the same speed rating as the originals, so ask your installer what your vehicle maker allows and what the lower rating would limit. Type both sizes with their codes and the calculator raises that question for you.
Does tire size affect the speedometer?
Yes. The speedometer counts how fast the wheels turn, so a shorter tire makes it read high and a taller one makes it read low. Put a 215/70R16 winter set on a car built for 225/65R17 and an indicated 100 km/h is really about 97.7. The odometer is off by the same share: about 977 km driven for every 1,000 it shows.
What does the middle number on a tire size mean?
It's the aspect ratio: the sidewall's height as a percentage of the tire's width. On a 225/65R17 the sidewall is 65% of 225 mm, or 146.25 mm, which the calculator shows as 146.3. Go to a 215/70R16 and the sidewall grows to 150.5 mm even though the tire is narrower. Both figures are nominal; a particular tire can measure a little differently.
What does XL mean on a tire?
Extra Load, sometimes marked REINFORCED: a tire built stronger than the standard version of the same size, and its load index says how much it's rated to carry. Switching to or from XL? Ask your installer what pressure the XL tire should run on your car. The pressure on your door placard was set for the tires the car was built with.
How do I read the date code on a tire?
Find the tire identification number on the sidewall, often right after DOT, and read its last four digits: week, then year. 4421 means week 44 of 2021, the week that began Sunday, October 31. Canada's tire rules count week 01 from the first Sunday of the year. Can't find it? The full number can be on one side of the tire only.
Where is the tire placard on my car?
Usually on the driver's side door pillar. Without a pillar there, look on the front edge of the rear door, then the back edge of the driver's door. It's headed Tire and Loading Information or Renseignements sur les pneus et le chargement, and the size sits under Original tire size, Dimensions originales du pneu, or just Size. Transport Canada also lists the glove box and the fuel door among the places your tire information label can be.
Why does my sidewall show kPa and kg?
Because Canada's tire rules require it. The maximum pressure moulded on the sidewall must be in kilopascals and the maximum load in kilograms; psi and pounds are optional extras. Neither is a target. Transport Canada is blunt about the pressure: don't use the one on the tire, it's the maximum. Use the one on your tire information label.
What does 31x10.50R15 mean?
It's a flotation size, written in inches: about 31 inches tall and 10.50 wide, a radial for a 15-inch wheel. In millimetres that's 787.4 tall overall. The calculator reads flotation and LT-metric sizes side by side, so you can set one against something like LT245/75R16, which works out to 773.9 mm, or 13.5 mm shorter.
Does anything I type get saved or sent?
No. The arithmetic runs in your browser, and nothing you type is sent anywhere or stored. There's no account to make. Print and Copy summary are the only ways to keep a result, and both stay with you.
Tire size comparison: summer set against winter set
Put a 215/70R16 winter set beside a 225/65R17 summer or all-season set and three things move. The wheel drops an inch, and the sidewall grows from 146.3 mm to 150.5 mm. The third one matters most: the whole tire comes out 16.9 mm shorter. That's what your speedometer and odometer feel, 2.3% less road per turn.
The ratings move on their own. In that example the winter tire is load index 100 (800 kg) and speed rating T (190 km/h), against 102 (850 kg) and H (210 km/h) on the other set. Whether that's fine for your car is your vehicle maker's call, printed on the door placard and in the owner's manual. That's why the calculator lists questions instead of answers. A good installer can look at the car. We can only read the sidewall.
Sources and last checked
Speed ratings come from the U.S. Tire Manufacturers Association's Tire Care and Safety guide and its Tire Information Service Bulletin Vol. 58 No. 1, and the km/h figures match UN Regulation No. 30. Load indexes 60 to 120 come from UN Regulation No. 30 and 121 to 130 from UN Regulation No. 54, as published in the EU's Official Journal in 2008; pounds are our conversion to the nearest pound. The Canadian rules come from the Motor Vehicle Tire Safety Regulations (kPa and kg on the sidewall, the date code, the winter tire definition), Transport Canada's TSD 139 Revision 1 and TSD 110 Revision 2 (mandatory from November 1, 2026), and Transport Canada's "Riding On Air" and "Using winter tires" pages. Provincial rules: quebec.ca's winter tire requirements, B.C.'s Motor Vehicle Act Regulations s.7.162 and its pages on winter tire and chain routes and passenger vehicle tire requirements, and ontario.ca's winter driving page.
We took the chart rows from those 2008 regulation texts and the association's own guide and bulletin. We didn't use the Tire and Rim Association's Year Book.
Chart data version 2026-10-07. Last checked October 8, 2026.
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Bookmark this page for the next changeover. It keeps nothing you type, so print the comparison or copy the summary before you head to the shop.