Metric to inch tire size converter
A 265/75R16 tire stands 31.65 inches tall and 10.43 inches wide on a 16-inch rim, so its flotation code is 31.65x10.43R16. Convert either notation both ways and compare a second size if you like. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Size
- 265/75R16
- Source format
- metric
- Metric size
- 265/75R16
- Inch size
- 31.65x10.43R16
- Construction
- R
Metric sidewall codes and inch flotation codes describe the same torus in two dialects. A size such as 265/75R16 names the section width in millimetres, the sidewall as a percent of that width, and the rim in inches. A size such as 31x10.50R15 names overall diameter and section width in inches on the same rim. This metric to inch tire size converter applies the exact 25.4 millimetre inch both ways, prints diameter and width in both unit systems, and optionally compares a second size so you can see whether a catalog flotation tire is actually equivalent or only close.
Metric codes, inch flotation codes, and the geometry that links them
The two codes on a light-truck or off-road sidewall are not two different tires. A metric ISO or ETRTO size such as 265/75R16 names the section width in millimetres, the aspect ratio as the sidewall height in percent of that width, a construction letter, and the rim diameter in inches. An inch flotation size such as 31x10.50R15 names the overall diameter in inches, the section width in inches, and the same rim diameter.
Both describe one circular carcass sitting on a rim, with two sidewalls stacked on that rim. The international inch is exactly 25.4 millimetres, so the identities are algebraic rather than empirical. From a metric code the sidewall height is width times aspect over one hundred, and overall diameter is the rim converted to millimetres plus two sidewalls.
From a flotation code the sidewall is half of overall diameter minus rim, and the aspect ratio is that sidewall as a percent of section width. This converter applies those identities in both directions and prints overall diameter and section width in millimetres and inches so you can see whether a catalog thirty-one inch tire is actually the same as your 265/75R16, or only close. It does not invent a load index, a speed rating, or a brand equivalent; those markings are independent of the geometry.
It also does not pick a marketing-rounded warehouse size that a shelf happens to stock. You get the true converted dimensions and a conventional code rounded to the requested decimals, which is the honest input for a later comparison against a candidate SKU.
Input contract, both directions, comparison fields, and errors
A slash marks a metric code (265/75R16, P215/60R16, LT265/75R16). An x marks an inch flotation code (31x10.50R15, 35x12.50R17). Optional prefixes P, LT, ST, T, and C are stripped.
The construction letter may be R, B, D, or a dash; a missing letter is treated as radial R. Optional decimals is an integer from zero to four and defaults to two; it rounds every numeric field and the flotation code. Optional compare is a second size in either notation.
Widths, aspects, and rims outside the published ranges fail the same way, as does a flotation size whose overall diameter is not greater than the rim, because that would make a non-positive sidewall.
Where a metric to inch tire size converter earns its keep
Off-road and light-truck owners meet both dialects on the same invoice: the door sticker is metric, the mud-terrain catalog is flotation, and a shop will not guarantee clearance until someone has compared overall diameter rather than guessed from the leading thirty-one. Fleet and rental desks keep mixed inventories; feeding a metric park tire and a flotation spare into compare produces a briefing of diameter and width deltas plus the speedometer error before a vehicle leaves the yard.
Cross-border trips add another reason: a European sidewall in millimetres has to sit next to a North American flotation listing without a silent unit mistake. Failed validation does not consume balance. Keep requests small, pin the rounded millimetre and inch figures in tests, and you get a reproducible conversion without standing up a tire-database.
If you later need revolutions per kilometre from a single metric code, load-index capacity, or a brand-equivalent lookup, treat those as separate search intents rather than stretching this converter past geometry.
What you can do with it
Door-sticker metric to catalog flotation
Convert 265/75R16 on the placard into 31.65x10.43R16 and compare that geometry with a 31x10.50R16 mud-terrain listing before you buy.
Importer and shop fitment checks
Show a customer that the inch flotation SKU is inside or outside the three-percent diameter band versus the metric size already on the truck.
FAQ
How do I convert a metric tire size to an inch flotation size?
Send size as a metric code such as 265/75R16.
How do I convert an inch flotation size back to metric?
Send size as a flotation code such as 31x10.50R15. Aspect ratio is 100×(overall diameter − rim) / (2×width).
What does the optional compare field do?
compare accepts a second size in either notation.
Is 265/75R16 the same as 31x10.50R16?
Not exactly. 265/75R16 is about 31.65 inches tall and 10.43 inches wide. A 31x10.50R16 is a nearby catalog flotation size; use compare to see the actual diameter and width deltas instead of assuming they match.
What does the metric to inch tire size converter cost?
The browser tool is free and runs locally.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/travel/metric-to-inch-tire \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"size":"265/75R16"}'const res = await fetch("https://api.kit.forhosting.com/travel/metric-to-inch-tire", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"size": "265/75R16"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/travel/metric-to-inch-tire",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"size": "265/75R16"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/travel/metric-to-inch-tire", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"size":"265/75R16"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"size":"265/75R16"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/travel/metric-to-inch-tire", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"size": "265/75R16"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "travel.metric_to_inch_tire",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_width_mm | 500 |
max_diameter_in | 55 |
max_decimals | 4 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Input contract, both directions, comparison fields, and errors
Send a JSON body with size, a string in either notation. When it is present the response adds the other tire's diameter and width, the millimetre and inch deltas, the percent changes, the implied speedometer error if you replace the first size with the second, and diameter_within_3_pct, which is true when the overall-diameter change stays inside the usual three percent fitment band. Missing size, an empty string, a non-string, or a token that matches neither pattern fails with invalid_input naming the field and is not billed. On success the body echoes the cleaned size, names the detected source_format as metric or inch, and returns metric_size, inch_size, construction, rim_inches, aspect_ratio, section width and overall diameter in both millimetres and inches, both sidewalls, both circumferences, and the exact millimetres-per-inch factor 25.4 so a client can reprint the calculation.
Where a metric to inch tire size converter earns its keep
Because this capability is a pure parse engine, the browser tool is free and a successful API call costs the published $0.002 base price with no model tokens and no outbound catalog service.
Integration use cases
Fleet mixed-inventory briefing
Feed a metric park tire and a flotation spare into compare and archive diameter, width, and speedometer-error JSON next to the vehicle file.