How do you calculate gear inches?
Multiply the gear ratio by the wheel's overall diameter in inches. A 46-tooth chainring driving a 17-tooth cog is a ratio of 46 ÷ 17 = 2.706. A 700×28 wheel and tire stand 26.69 inches tall. So 2.706 × 26.69 = 72.2 gear inches. The name comes from the high-wheeler: a 72.2-inch gear moves you as far per pedal turn as a penny-farthing with a 72.2-inch front wheel. Multiply by π and you get the distance itself, 5.76 meters per crank revolution. That's meters of development, the metric way of saying the same thing, and the chart above switches to it.
Gear inches exist because a bare ratio ignores the wheel. A 2.7 gear on a 20-inch BMX wheel is a much easier gear than a 2.7 on a road bike. Fixed-gear and singlespeed riders, who live with one gear, still compare bikes this way, and so does anyone moving a gear between wheel sizes.
Which wheel diameter do gear inches use?
The real one, tire included, and this is where gear-inch charts disagree. Older charts multiply every road gear by a nominal 27 inches; others use 26.3, a 700×23. Each is right for the tire it assumed. The same 48×17 on 700c wheels:
| Tire | Overall diameter | 48 × 17 in gear inches |
|---|---|---|
| 700 × 23 | 26.30 in | 74.3 |
| 700 × 25 | 26.46 in | 74.7 |
| 700 × 28 | 26.69 in | 75.4 |
| 700 × 32 | 27.01 in | 76.3 |
| 700 × 35 | 27.24 in | 76.9 |
| 700 × 40 | 27.64 in | 78.0 |
Overall diameter = rim bead-seat diameter (622 mm) + twice the tire width. A "27-inch" chart is accurate for a 700×32 and reads high for narrower tires.
So a chart that says 48×17 is a 76.3-inch gear is right for a 700×32 rider and reads high for someone on 700×23s, who is really riding 74.3. That's less than a cog tooth, but enough to matter when you compare your gear with a friend's. The calculator uses your tire width. Its wheel sizes run from 20-inch BMX through 650c and 27-inch to 29er.
Gear inch chart for fixed gear and singlespeed
The common fixed-gear range on 700×28 tires, chainrings down the side and cogs across the top. The small number is the skid patch count, explained below. The chart above the article rebuilds this for your tire and prints on one page.
| Ring | 14t | 15t | 16t | 17t | 18t | 19t |
|---|---|---|---|---|---|---|
| 42t | 80.1 1 | 74.7 5 | 70.1 8 | 65.9 17 | 62.3 3 | 59.0 19 |
| 44t | 83.9 7 | 78.3 15 | 73.4 4 | 69.1 17 | 65.2 9 | 61.8 19 |
| 46t | 87.7 7 | 81.9 15 | 76.7 8 | 72.2 17 | 68.2 9 | 64.6 19 |
| 47t | 89.6 14 | 83.6 15 | 78.4 16 | 73.8 17 | 69.7 18 | 66.0 19 |
| 48t | 91.5 7 | 85.4 5 | 80.1 1 | 75.4 17 | 71.2 3 | 67.4 19 |
| 49t | 93.4 2 | 87.2 15 | 81.7 16 | 76.9 17 | 72.7 18 | 68.8 19 |
| 50t | 95.3 7 | 89.0 3 | 83.4 8 | 78.5 17 | 74.1 9 | 70.2 19 |
Gear inches on 700×28 (26.69 in overall); small number = skid patches, skidding with one foot forward. Computed by the same engine as the calculator.
What gear inches should I ride on a fixed gear?
Ask a fixed-gear forum and you'll get a range: 65 to 75 inches for city riding, 70 if you're not sure. That's a fair average and a poor answer, because the right gear depends on two numbers a range can't know: your power and your steepest hill. Here's what common gears do for a 75 kg (165 lb) rider holding 200 watts:
| Gear | Gear inches | 90 rpm | Spin-out | Seated up to | On a 5% hill |
|---|---|---|---|---|---|
| 42 × 19 | 59.0 | 15.8 mph | 21.1 mph | 4.0% | 51 rpm |
| 42 × 17 | 65.9 | 17.7 mph | 23.5 mph | 3.4% | 46 rpm |
| 44 × 17 | 69.1 | 18.5 mph | 24.7 mph | 3.1% | 44 rpm |
| 46 × 17 | 72.2 | 19.3 mph | 25.8 mph | 2.8% | 42 rpm |
| 48 × 17 | 75.4 | 20.2 mph | 26.9 mph | 2.6% | 40 rpm |
| 48 × 16 | 80.1 | 21.4 mph | 28.6 mph | 2.3% | 38 rpm |
| 49 × 15 | 87.2 | 23.3 mph | 31.1 mph | 1.8% | 35 rpm |
700×28. Spin-out = speed at 120 rpm, roughly where legs top out; on a fixed gear you can't coast, so it's your downhill speed limit. "Seated up to" = the steepest grade where 200 W still turns 60 rpm (Martin power model, 75 kg rider + 10 kg bike and kit, hands on the hoods).
Every gear that climbs well spins out early on the flat. The forum favorite, 46 × 17 at 72.2 inches, cruises at 19.3 mph at 90 rpm, but past a 2.8% grade you're out of the saddle. On a 5% hill it's 42 rpm, a standing grind. Even a 59.0-inch gear only stays seated up to 4.0%. That's why riders in hilly cities run lower gears than riders on flat routes, and why the hill check in the calculator asks for your steepest hill rather than your average one.
To stay seated at 60 rpm up a 5% grade, a 200-watt rider needs about a 49-inch gear (46×25). In that gear, 17.5 mph on the flat is already 120 rpm. A singlespeed can coast downhill, so it can be geared that low without the downhill penalty, though flat roads still feel slow. A fixed gear can't coast at all, so fixed riders stand up on the climbs.
How many skid patches does my gear have?
A skid patch is a spot on the rear tire that ends up on the ground when you lock your legs to skid a fixed gear. With the cranks level, the wheel can only stop in a few positions, and those spots wear flat. To count them, reduce the gear ratio to lowest terms; the bottom number is the patch count. 46×17 won't reduce, so it has 17 patches. 48×16 reduces to 3/1, so it has one: every skid lands on the same spot, and that tire won't last.
If you can skid with either foot forward, the half-turn positions count too. That doubles the patches, but only when the reduced chainring number is odd. 46×16 reduces to 23/8, and 23 is odd, so 8 patches become 16. 48×19 won't reduce and 48 is even, so it stays at 19. Charts that double every gear are wrong about half of them. The calculator's checkbox handles it.
Patch count is free to choose, because the same gear can be built many ways. Here are the 8 ways to make a gear within 1.5% of 72.2 inches on 700×28, from 3 patches to 38:
| Gear | Gear inches | Skid patches | Skidding either foot |
|---|---|---|---|
| 51 × 19 | 71.6 | 19 | 38 |
| 49 × 18 | 72.7 | 18 | 36 |
| 43 × 16 | 71.7 | 16 | 32 |
| 41 × 15 | 73.0 | 15 | 30 |
| 52 × 19 | 73.1 | 19 | 19 |
| 46 × 17 | 72.2 | 17 | 17 |
| 40 × 15 | 71.2 | 3 | 3 |
| 48 × 18 | 71.2 | 3 | 3 |
Every chainring 40–52 and cog 14–20 within ±1.5% of 46×17 on 700×28.
If you skid a lot, pick from the top of the table. If you have a brake and rarely skid, patches don't matter much. Choose the combination that fits your chain and dropouts; the chain length calculator's singlespeed mode works out the links and how far the wheel has to slide back.
Meters of development and junior rollout limits
Racing writes gear limits as development, because a tape measure can check it: put the bike in its biggest gear, roll it backward through one full crank turn and measure the distance. That's the rollout test. USA Cycling still limits junior gears on the track:
| Ages | Max rollout | Largest ring, 14t cog | Largest ring, 15t cog | Largest ring, 16t cog |
|---|---|---|---|---|
| 15–16 | 6.93 m | 46t | 49t | 52t |
| 13–14 | 6.45 m | 43t | 46t | 49t |
| 10–12 | 6.05 m | 40t | 43t | 46t |
USA Cycling junior track limits; 17–18 is unrestricted, and there are no junior limits on the road, in cyclocross or in MTB (road limits ended in 2023, after the UCI dropped its own). Largest rings computed on 700×23 tires; a wider tire rolls farther.
USA Cycling prints example gears beside the limits and calls them suggestions, which is the right word. On 700×23 tires, the 50×16 listed beside the 13–14 limit rolls 6.56 m, more than the 6.45 m next to it. Roll the bike out before the race. The check after the race decides legality.
In 2025 the UCI planned a trial capping pro road-race gearing at 10.46 meters of development, which is what a 54×11 covers on 28 mm tires (10.46 m by this calculator). On 30 mm tires the same 54×11 rolls 10.52 m, over the cap. With SRAM's 10-tooth cog on 28s, nothing bigger than a 49-tooth chainring would fit. The trial was suspended by Belgium's competition authority in October 2025, and the suspension was upheld on appeal in May 2026.
Gain ratio: gear inches with your crank length in
Gear inches ignore the cranks, but a longer crank gives more leverage, and that makes the same gear feel easier. Sheldon Brown's gain ratio accounts for it: wheel radius ÷ crank length × gear ratio. The result is how far the bike moves for each inch the pedal moves, and it has no units. For 46×17 on 700×28:
| 165 mm cranks | 170 mm cranks | 172.5 mm cranks | 175 mm cranks |
|---|---|---|---|
| 5.56 | 5.40 | 5.32 | 5.24 |
Higher gain = harder gear. Gain ratio = (wheel radius ÷ crank length) × ratio.
Going from 175 mm to 165 mm cranks raises the gain about as much as going from a 17-tooth cog to a 16. If you change crank length, expect the gear to feel different. Whether shorter cranks cost you power (they barely do) is covered on the crank length calculator.
How the numbers are calculated
Gear inches = (chainring ÷ cog) × (rim bead-seat diameter + 2 × tire width) ÷ 25.4. Development is gear inches × π, in meters. Gain ratio and the skid patch rule follow Sheldon Brown's definitions. The geometric diameter matches published rollout charts (700×25 computes to 2,111 mm around, the wheel circumference figure) and reproduces the UCI's 10.46 m for 54×11 on 28 mm tires. The hill check uses the same Martin et al. power model as the power ↔ speed calculator: sea-level air, road tires, hands on the hoods. Real rollout varies with tire pressure and load by about a percent, which is enough to matter at a junior gear check, so measure there. For geared bikes, the gear ratio calculator shows gear inches for every gear at once.