Snow Chain Tire Size Chart: Finding the Right Chain Size From Your Tire Sidewall

To find the right snow chain size, read the full tire size printed on your tire sidewall, such as 225/65R17, and look up that exact size in the chain manufacturer's fitment chart. The chart turns your tire size into that brand's chain size code. Three numbers decide chain size: tire width, aspect ratio and rim diameter. The load index and speed rating that follow them do not change chain size. Before you buy, also check your owner's manual for vehicle chain clearance limits, because a chain can match the tire and still not fit the vehicle.

What size tire chains do I need?

You need the chain size that the chain manufacturer lists for your exact tire size. Snow chains are sized by tire dimensions, not by vehicle model alone. Use this process:

1. Find the tire size on the sidewall of the tire that will carry the chains. It is usually printed in large characters, for example P225/65R17 102H or LT265/70R17 121/118S.
2. Write down the full size, including any prefix (P or LT) and suffix (LT on flotation sizes). The key part is the width, aspect ratio and rim diameter, such as 225/65R17.
3. Look up that exact size in the snow chain size chart for the chain model you are considering.
4. Note the chain size code the chart gives you. Codes are specific to each brand and product line.
5. Check the vehicle owner's manual for chain restrictions, such as a required clearance class, chains on the drive axle only, or no chains with certain wheel and tire sizes.
6. If your tire size is not listed, do not pick the nearest size. Choose a chain model whose chart includes your size, or ask the manufacturer.

If your vehicle has different tire sizes front and rear, read the size on the axle that will get the chains. That is normally the drive axle, unless the vehicle manual says otherwise.

How do you read tire size markings on the sidewall?

A tire size marking is a code made of dimensions, a construction letter and service ratings. For snow chain sizing, only the dimensions matter. The table breaks down the common metric marking P225/65R17 102H.

Part of marking	Example	What it means	Type	Relevant to chain size?
Prefix	P	P-metric passenger tire. LT means light truck. No prefix usually means a European metric size.	Tire category	Indirectly. Write it down, because some charts list P, LT and metric versions separately.
Section width	225	Nominal tire width in millimetres, measured sidewall to sidewall.	Dimension (mm)	Yes
Aspect ratio	65	Sidewall height as a percentage of section width. Here it is 65% of 225 mm.	Ratio (%)	Yes
Construction	R	Radial construction.	Construction type	No
Rim diameter	17	Diameter of the wheel the tire fits, in inches.	Dimension (in)	Yes
Load index	102	Coded maximum load per tire at its specified pressure.	Performance rating	No
Speed rating	H	Coded maximum sustained speed the tire is rated for.	Performance rating	No

Metric tire sizes mix units. Width is in millimetres and rim diameter is in inches. You must convert one of them before you can calculate tire dimensions.

P-metric, European metric and LT metric sizes

P-metric, European metric and LT metric tire sizes all use the same width/aspect ratio/rim layout, such as 225/65R17 or LT245/75R16. They can carry different load ratings and may have slightly different actual dimensions. Some chain manufacturer fitment charts list them as separate rows. When the chart separates them, match the prefix as well as the numbers.

Flotation (inch) tire sizes

Flotation sizes, common on trucks and off-road vehicles, give dimensions directly in inches. In 31x10.50R15LT, 31 is the overall diameter in inches, 10.50 is the section width in inches, R means radial, 15 is the rim diameter in inches, and LT means light truck. Because the overall diameter is stated directly, the sidewall height is (31 − 15) ÷ 2 = 8 in. Look up flotation sizes in the chart exactly as written. A chart may list 31x10.50R15 but not a metric size that seems similar.

Sidewall markings that do not change chain size

Several other sidewall markings matter for tire use but not for choosing a snow chain size:

• Load index and speed rating (for example 102H): service limits, not dimensions.
• LT load range (for example Load Range E): load and pressure capacity.
• Maximum inflation pressure: a tire limit, not the recommended pressure for your vehicle.
• DOT code: identifies the manufacturer, and its last four digits give the week and year of manufacture.
• UTQG ratings (treadwear, traction, temperature): comparative performance grades.
• M+S and the three-peak mountain snowflake symbol: winter or all-weather designations. They do not replace chains where chains are required, and they do not change chain size.

How do width, aspect ratio and rim diameter affect tire dimensions?

Tire width, aspect ratio and rim diameter together determine a tire's calculated sidewall height, overall diameter and circumference. These dimensions describe how much tire a snow chain has to wrap around. Use these formulas for metric sizes:

• Sidewall height (mm) = section width (mm) × aspect ratio ÷ 100
• Overall diameter (mm) = rim diameter (in) × 25.4 + 2 × sidewall height (mm)
• Circumference (mm) = overall diameter (mm) × π (about 3.1416)

Worked example for 225/65R17:

1. Sidewall height: 225 × 65 ÷ 100 = 146.25 mm.
2. Rim diameter in millimetres: 17 × 25.4 = 431.8 mm.
3. Overall diameter: 431.8 + 2 × 146.25 = 724.3 mm, or about 28.5 in.
4. Circumference: 724.3 × 3.1416 ≈ 2,275 mm, or about 89.6 in.

Tire size comparison: calculated dimensions

The table compares the calculated geometry of several common tire sizes. Values are rounded and based on nominal markings, not measured tires.

Tire size	Width (mm)	Sidewall height (mm)	Overall diameter (mm / in)	Circumference (mm)
225/65R17	225	146.3	724.3 / 28.5	2,275
225/60R17	225	135.0	701.8 / 27.6	2,205
235/65R17	235	152.8	737.3 / 29.0	2,316
265/55R17	265	145.8	723.3 / 28.5	2,272
215/70R16	215	150.5	707.4 / 27.9	2,222
245/45R18	245	110.3	677.7 / 26.7	2,129

What the comparison shows:

• Changing only the aspect ratio (225/65R17 vs 225/60R17) keeps the width the same. The sidewall is 11.25 mm shorter, the overall diameter is 22.5 mm smaller, and the circumference is about 70 mm shorter.
• Changing only the width (225/65R17 vs 235/65R17) also changes sidewall height, because aspect ratio is a percentage of width. The wider tire is both wider and taller.
• Similar diameter does not mean similar chain size. 265/55R17 and 225/65R17 have nearly the same calculated diameter, but the first is 40 mm wider. The chain's cross chains must span that extra tread width.
• A larger rim does not always mean a larger tire. 245/45R18 sits on a bigger wheel than 225/65R17, but its low aspect ratio gives it a smaller overall diameter.

Why these dimensions matter for snow chain fit

A snow chain has two main dimensional jobs. The side chains or cables must run around the tire's circumference on the inner and outer sidewalls. The cross chains or traction elements must reach across the tread width and onto the shoulders. Circumference and overall diameter mostly determine side chain length. Width and the tire's cross-section shape mostly determine cross chain length. A chain that is too small will not close or will sit too tight. A chain that is too large cannot be tensioned properly and may move or strike the vehicle.

Calculated geometry vs actual tire dimensions

Calculated tire geometry is an estimate from nominal markings. It is not a measurement of the tire on your vehicle. Actual dimensions differ for several reasons:

• Brand and model differences: two tires marked 225/65R17 can differ slightly in real width and diameter because of construction and tread design.
• Measuring rim width: section width is specified on a standard measuring rim. A wider or narrower wheel changes how wide the tire actually sits.
• Tread wear: a worn tire has a smaller diameter than a new one of the same size.
• Inflation and load: pressure and vehicle weight change the tire's mounted shape and its loaded height.
• Tread and shoulder shape: aggressive shoulders or squared profiles affect how a chain lies on the tire.

For these reasons, chain makers publish charts by tire size marking, not by calculated diameter. Use the calculation to understand why two sizes differ, not to decide that a chain listed for one size will fit another.

How to use a snow chain size chart

A snow chain size chart, also called a tire chain fitment chart, lists tire sizes and the chain size code that fits each one for a specific chain model. To use it correctly:

1. Use the chart for the exact chain product you plan to buy. Charts differ between brands and between product lines from the same brand.
2. Find your rim diameter section, often grouped as 15, 16, 17 inches and so on.
3. Find the row that matches your width and aspect ratio exactly, such as 225/65.
4. Read the chain size code in that row.
5. Check any notes in the chart about clearance class, vehicle restrictions or tire types such as LT or flotation sizes.

Why one chain size fits several tire sizes

One chain size code often covers several tire sizes because chains are built with adjustment range and tensioning. Tire sizes with similar circumference and width can fall within the same chain's working range. This is why a snow chain size chart may list 215/70R16 and 225/65R17 under the same code in one product line. Whether two specific sizes share a code depends entirely on that product's design. Only the chart can confirm it.

Chain size codes are brand-specific

Chain size codes are not universal. A number or letter code from one manufacturer does not correspond to the same tire range in another manufacturer's line. When you replace or compare chains, start again from your tire size and the new product's chain manufacturer fitment chart. Do not carry a size code over from an old set.

What a snow chain size calculator or size finder can and cannot tell you

A snow chain size calculator or chain size finder is useful for converting a tire marking into dimensions or for looking up a code, but it is only as reliable as the data behind it. Tools that calculate diameter and circumference show the same geometry described above. They help you understand how a size compares with another. Tools that ask for your tire size and return a chain code are a digital version of a manufacturer's chart, and they are reliable only for the product line they were built for.

A size finder that suggests chains by vehicle model needs extra care. Vehicles are often sold with several wheel and tire options, and owners may fit non-original sizes. Always confirm that the result matches the tire size actually printed on your sidewall.

Tire and chain size compatibility vs vehicle chain clearance

Tire and chain size compatibility means the chain fits the tire. Vehicle chain clearance means there is enough space around the tire for the chain to turn without hitting the vehicle. These are separate checks, and both must pass.

• Owner's manual instructions: many manuals state whether chains may be used, which axle to use them on, and whether only low-profile or limited-clearance chains are allowed. Some prohibit chains with certain optional wheel and tire sizes.
• Clearance classes: some manuals and chain products refer to SAE clearance classes. Class S is intended for vehicles with restricted wheel-well clearance. If your manual names a class, choose a chain that meets it.
• Non-original tire sizes: fitting a wider or taller tire than the vehicle came with reduces the space around it. A chain can then match the new tire size and still contact the suspension, brake lines or bodywork.

Clearance depends on the vehicle, so a tire size chart alone cannot confirm it. Follow the manual's limits when they apply.

Common snow chain sizing mistakes

• Reading the size from the vehicle documents instead of the tire: the tires fitted may not be the original size.
• Choosing the closest listed size: a size that looks close, such as 225/60R17 instead of 225/65R17, has a different circumference and width.
• Matching only the overall diameter: width also affects cross chain length, as the 265/55R17 vs 225/65R17 comparison shows.
• Treating load index or speed rating as part of the size: these are ratings, not dimensions.
• Assuming chain codes match across brands: each brand uses its own chain size codes.
• Ignoring the owner's manual: a correctly sized chain may still be unsuitable if the vehicle has limited clearance.