Chainring Size Calculator
Enter the speed you want to ride, your cadence, the rear cog and your wheel size. The calculator gives the chainring teeth, the nearest common ring and the speed, ratio and gear inches it gives you.
- Chainring teeth
- Gear ratio
- Gear inches
Cadence is how many times your pedals turn in a minute.
Chainring = speed × cog ÷ (cadence × wheel). To ride 40 km/h at 90 rpm in a 15 tooth cog on 700 × 28c wheels, you need about 52 teeth. A 52 tooth ring gives a 3.47 ratio and about 93 gear inches.
Chainring speed chart
At 90 rpm, 700 × 28c. Search for a ring.
| Chainring | 11 cog (km/h) | 15 cog (km/h) | 21 cog (km/h) | 28 cog (km/h) |
|---|---|---|---|---|
| 30 | 31.5 | 23.1 | 16.5 | 12.4 |
| 32 | 33.6 | 24.6 | 17.6 | 13.2 |
| 34 | 35.7 | 26.1 | 18.7 | 14 |
| 36 | 37.7 | 27.7 | 19.8 | 14.8 |
| 40 | 41.9 | 30.8 | 22 | 16.5 |
| 42 | 44 | 32.3 | 23.1 | 17.3 |
| 46 | 48.2 | 35.4 | 25.3 | 18.9 |
| 50 | 52.4 | 38.4 | 27.5 | 20.6 |
| 52 | 54.5 | 40 | 28.6 | 21.4 |
| 53 | 55.6 | 40.8 | 29.1 | 21.8 |
km/h.
Chainring and speed
15 cog, 90 rpm. Slide the chainring.
The ring and cog are drawn with their teeth.
How to size a chainring
Speed to teeth. Step through it.
Speed
Target.
Check your crank's bolt circle before ordering.
Compact, semi-compact or standard
Road chainsets. Compare them.
Easy climbing.
All round.
Racing.
Smaller rings make climbing easier, larger rings give top speed.
Before you buy
Drivetrain checks. Tick each item.
Tick each item as you go.
Change the chain when you change rings so the teeth wear evenly.
What you get
Gear sizing. Each tile explains one result.
Ring.
Ring ÷ cog.
Equivalent wheel.
km/h.
Per pedal turn.
Gear inches compare gears across different wheel sizes.
Frequently Asked Questions
No question matches that search.
What size chainring do I need?
Multiply your target speed by the cog and divide by cadence times wheel circumference.
What chainring for forty kilometres an hour?
About fifty two teeth with a fifteen tooth cog at ninety rpm.
Does a bigger chainring make me faster?
It lets you go faster at the same cadence, but needs more force.
What is a compact chainset?
A fifty and thirty four tooth pair that makes climbing easier.
What chainring size for a mountain bike?
Most single ring mountain bikes use thirty to thirty four teeth.
What are gear inches?
The diameter of an old style wheel that would roll the same distance.
Can I fit any chainring to my crank?
No. The bolt circle diameter and chain width must match.
The gear you want
Set your speed and cadence and find the chainring that puts you right where you like to ride.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.