Learn about the international standard for labelling the size of tires
International standards have had a positive impact on the cycling industry. This article aims to explain modern tire sizes, how they're designated, and how to convert from older systems.
What is ISO 5775?
ISO 5775 is the international standard for labelling the size of bicycle tires and rims. It was originally developed by the European Tire and Rim Technical Organisation (ETRTO); and has since been licensed to the International Organization for Standardization (ISO).
How are tire sizes designated?
This system replaces overlapping informal systems that ambiguously distinguished between sizes. Previously, nominal dimensions were used which were interpreted in different ways by different countries and manufacturers – causing a problem for the end-user.
Tire sizes according to this system are designated with the following format, where TT stands for the thickness of the inflated tire minus any tread, and TD for the inner diameter of the tire when it's mounted on the rim.
Where can measurements be found?
The thickness of the tire is measured across its tread, while the diameter of the rim is measured up to its bead. Both are measured in millimetres. A marking can also be found printed on the sidewalls of the tire.
Which other tire sizing systems exist?
There exists several other systems, but none are international standards. To learn more about these sizing systems, please visit our articles covering each topic individually.
Why does BikeCalc not provide all tire sizing systems?
BikeCalc tries to provide a quality product that all cyclists can trust. We recognize that standards ensure a reliable basis for everyone to share the same expectations about how a product is intended to function; and so we make it our responsibility to follow international standards for everyone's benefit.
How to convert older tire sizes?
Older tire sizes can be converted to ISO 5775 designations with the help of the following conversion table.
| 40 - 305 | 16 × 1.50 | - |
| 44 - 305 | 16 × 1.65 | - |
| 47 - 305 | 16 × 1.75 | - |
| 50 - 305 | 16 × 2.00 | - |
| 54 - 305 | 16 × 2.10 | - |
| 57 - 305 | 16 × 2.25 | - |
| 62 - 305 | 16 × 2.40 | - |
| 23 - 355 | 18 × 0.90 | - |
| 25 - 355 | 18 × 1.00 | - |
| 28 - 355 | 18 × 1.10 | - |
| 30 - 355 | 18 × 1.20 | - |
| 32 - 355 | 18 × 1.25 | - |
| 35 - 355 | 18 × 1.35 | - |
| 37 - 355 | 18 × 1.40 | - |
| 40 - 355 | 18 × 1.50 | - |
| 44 - 355 | 18 × 1.65 | - |
| 47 - 355 | 18 × 1.75 | - |
| 50 - 355 | 18 × 2.00 | - |
| 23 - 406 | 20 × 0.90 | - |
| 25 - 406 | 20 × 1.00 | - |
| 28 - 406 | 20 × 1.10 | - |
| 30 - 406 | 20 × 1.20 | - |
| 32 - 406 | 20 × 1.25 | - |
| 35 - 406 | 20 × 1.35 | - |
| 37 - 406 | 20 × 1.40 | - |
| 40 - 406 | 20 × 1.50 | - |
| 44 - 406 | 20 × 1.65 | - |
| 47 - 406 | 20 × 1.75 | - |
| 50 - 406 | 20 × 2.00 | - |
| 54 - 406 | 20 × 2.10 | - |
| 57 - 406 | 20 × 2.25 | - |
| 62 - 406 | 20 × 2.40 | - |
| 23 - 489 | 22 × 0.90 | - |
| 25 - 489 | 22 × 1.00 | - |
| 28 - 489 | 22 × 1.10 | - |
| 30 - 489 | 22 × 1.20 | - |
| 32 - 489 | 22 × 1.25 | - |
| 35 - 489 | 22 × 1.35 | - |
| 37 - 489 | 22 × 1.40 | - |
| 40 - 507 | 24 × 1.50 | - |
| 44 - 507 | 24 × 1.65 | - |
| 47 - 507 | 24 × 1.75 | - |
| 50 - 507 | 24 × 2.00 | - |
| 54 - 507 | 24 × 2.10 | - |
| 57 - 507 | 24 × 2.25 | - |
| 62 - 507 | 24 × 2.40 | - |
| 23 - 540 | 24 × 0.90 | - |
| 25 - 540 | 24 × 1.00 | - |
| 28 - 540 | 24 × 1.10 | - |
| 30 - 540 | 24 × 1.20 | - |
| 32 - 540 | 24 × 1.25 | - |
| 35 - 540 | 24 × 1.35 | - |
| 37 - 540 | 24 × 1.40 | - |
| 23 - 559 | 26 × 0.90 | - |
| 25 - 559 | 26 × 1.00 | - |
| 28 - 559 | 26 × 1.10 | - |
| 30 - 559 | 26 × 1.20 | - |
| 32 - 559 | 26 × 1.25 | - |
| 37 - 559 | 26 × 1.40 | - |
| 40 - 559 | 26 × 1.50 | - |
| 40 - 559 | 26 × 1.50 | - |
| 44 - 559 | 26 × 1.65 | - |
| 47 - 559 | 26 × 1.75 | - |
| 50 - 559 | 26 × 2.00 | - |
| 54 - 559 | 26 × 2.10 | - |
| 57 - 559 | 26 × 2.25 | - |
| 62 - 559 | 26 × 2.40 | - |
| 23 - 571 | - | 650 × 23 C |
| 25 - 571 | - | 650 × 25 C |
| 28 - 571 | - | 650 × 28 C |
| 32 - 571 | - | 650 × 32 C |
| 37 - 571 | - | 650 × 35 C |
| 40 - 571 | - | 650 × 38 C |
| 44 - 571 | - | 650 × 42 C |
| 47 - 571 | - | 650 × 45 C |
| 23 - 584 | - | 650 × 23 B |
| 25 - 584 | - | 650 × 25 B |
| 28 - 584 | - | 650 × 28 B |
| 32 - 584 | - | 650 × 32 B |
| 35 - 584 | 27.5 × 1.35 | - |
| 37 - 584 | 27.5 × 1.40 | 650 × 35 B |
| 40 - 584 | 27.5 × 1.50 | 650 × 38 B |
| 44 - 584 | 27.5 × 1.65 | 650 × 42 B |
| 47 - 584 | 27.5 × 1.75 | - |
| 50 - 584 | 27.5 × 2.00 | - |
| 54 - 584 | 27.5 × 2.10 | - |
| 57 - 584 | 27.5 × 2.25 | - |
| 62 - 584 | 27.5 × 2.40 | - |
| 23 - 590 | - | 650 × 23 A |
| 25 - 590 | - | 650 × 25 A |
| 28 - 590 | - | 650 × 28 A |
| 32 - 590 | - | 650 × 32 A |
| 37 - 590 | - | 650 × 35 A |
| 40 - 590 | - | 650 × 38 A |
| 44 - 590 | - | 650 × 42 A |
| 23 - 622 | 28 × 0.90 | 700 × 23 C |
| 25 - 622 | 28 × 1.00 | 700 × 25 C |
| 28 - 622 | 28 × 1.10 | 700 × 28 C |
| 30 - 622 | 28 × 1.20 | 700 × 30 C |
| 32 - 622 | 28 × 1.25 | 700 × 32 C |
| 35 - 622 | 28 × 1.35 | - |
| 37 - 622 | 28 × 1.40 | 700 × 35 C |
| 40 - 622 | 28 × 1.50 | 700 × 38 C |
| 44 - 622 | 28 × 1.65 | 700 × 42 C |
| 47 - 622 | 28 × 1.75 | 700 × 45 C |
| 50 - 622 | 28 × 2.00 | - |
| 54 - 622 | 28 × 2.10 | - |
| 57 - 622 | 28 × 2.25 | - |
| 62 - 622 | 28 × 2.40 | - |
| 50 - 622 | 29 × 2.00 | - |
| 54 - 622 | 29 × 2.10 | - |
| 57 - 622 | 29 × 2.25 | - |
| 62 - 622 | 29 × 2.40 | - |
| 23 - 630 | 27 × 0.90 | - |
| 25 - 630 | 27 × 1.00 | - |
| 28 - 630 | 27 × 1.10 | - |
| 30 - 630 | 27 × 1.20 | - |
| 32 - 630 | 27 × 1.25 | - |
| 35 - 630 | 27 × 1.35 | - |
| 23 - 635 | - | 700 × 23 B |
| 25 - 635 | - | 700 × 25 B |
| 28 - 635 | - | 700 × 28 B |
| 32 - 635 | - | 700 × 28 B |
| 37 - 635 | - | 700 × 35 B |
| 40 - 635 | - | 700 × 38 B |
| 44 - 635 | - | 700 × 42 B |
| 23 - 642 | - | 700 × 23 A |
| 25 - 642 | - | 700 × 25 A |
| 28 - 642 | - | 700 × 28 A |
| 30 - 642 | - | 700 × 30 A |
| 32 - 642 | - | 700 × 32 A |
| 37 - 642 | - | 700 × 35 A |
