Decode a load index, or find the one you need
The two- or three-digit number after a tire size — 91 in 225/65R91 — is not arbitrary. It maps to a specific maximum load capacity per tire, set by a standards table rather than a formula.
| Load index | lbs | kg |
|---|---|---|
| 87 | 1201 | 545 |
| 88 | 1235 | 560 |
| 89 | 1279 | 580 |
| 90 | 1323 | 600 |
| 91 | 1356 | 615 |
| 92 | 1389 | 630 |
| 93 | 1433 | 650 |
| 94 | 1477 | 670 |
| 95 | 1521 | 690 |
Getting a number you can act on
- 01Find the load index on the sidewall
It follows the rim diameter in the size designation, typically a two- or three-digit number immediately before the speed rating letter.
- 02Decode it to a load capacity
This gives the maximum weight that single tire can carry at its rated maximum pressure — not the vehicle's total capacity.
- 03Or work in the other direction from a target load
If you know how much weight each tire needs to carry — from a vehicle's GVWR divided across the axles, for instance — find the minimum index that covers it.
- 04Never go below the original equipment index
The index on the vehicle's tire placard is the minimum the vehicle was engineered around. Going lower, even if the tire otherwise fits, can under-rate the vehicle's actual load capacity.
Why load index is a table, not a formula
Unlike most of the arithmetic elsewhere in this tool section, load index capacity is not calculated from a physical relationship — it is a standards table published by bodies including the Tire and Rim Association, assigning a specific load figure to each index number.
The values increase roughly but not exactly exponentially as the index rises, reflecting the practical range of tire constructions rather than a clean mathematical curve. That is why this tool reproduces the table directly rather than approximating it with an equation — an approximation would be wrong at exactly the values that matter.
A higher load index does not mean a physically larger tire in every case. Two tires of the same size can carry different load indices depending on their internal construction and ply rating, which is why the index — not just the size — matters when confirming a replacement tire is adequate.
How to use this when replacing tires
- Find the original equipment load index on the vehicle's door-jamb placard, not the tire currently fitted if it may have been changed
- A replacement tire should match or exceed that index — never go lower
- Four-tire total capacity is not the same as vehicle GVWR — GVWR accounts for uneven load distribution and other factors
- A dual-rated tire (two numbers separated by a slash) shows single and dual-wheel-application capacity separately
- Load index and speed rating are independent figures — check both against the vehicle's requirement
Tire Load Index Calculator FAQ
What does tire load index mean?+
A code number that maps, via a published standards table, to the maximum load a single tire can carry at its rated maximum pressure.
What is load index 91 in pounds?+
1,356 lbs (615 kg) per tire, at the tire's rated maximum pressure.
Can I use a tire with a lower load index than the original?+
Not advisable. The original equipment load index reflects what the vehicle was engineered to carry safely — going lower under-rates the vehicle's actual load capacity even if the tire otherwise fits.
Is load index the same as tire size?+
No — it is a separate figure in the full size designation. Two tires of identical size can carry different load indices depending on internal construction.
How is load index different from vehicle GVWR?+
Load index is per tire; GVWR is the vehicle's total rated weight and accounts for load distribution and other factors, so simply multiplying tire capacity by four does not equal GVWR.
Standards and references behind these figures
The arithmetic on this page is fixed, but the boundaries and conventions around it come from published standards and manufacturer guidance. These are the documents they come from, so you can check them rather than take them on trust.
01The Tire and Rim Association — standards filing (NHTSA docket)TRA has been the US standardising body for tire and rim interchangeability since 1903; this filing sets out dimensional practice.↗Nominal sizes, not measured ones. Every figure here is calculated from the size marked on the sidewall. Real tires vary from nominal by a few millimetres between manufacturers, and more as tread wears or pressure changes. Use these numbers to plan and to sanity-check a quote — measure the actual tire before committing to a tight fitment.