Every gear on your bike in metres, inches and km/h, checked against Shimano, SRAM and Campagnolo's own compatibility documents. Then see what it does on a real climb.
The gear table tells you what each combination is. This part tells you what it does on a real gradient: the speed your power gives you, and the cadence that leaves you turning in your easiest gears. The steepest ramp decides the gearing, not the average, so both are here.
Uses the gearing of setup A above (and B, if you are comparing).
Physics model from Martin et al. (1998), validated against an SRM power meter to within 2.7 W. It assumes a paved road, no wind and a steady effort.
Five ways of describing the same thing: how far one turn of the pedals moves the bike. Each one answers a slightly different question. The example is the same in all five: a 34x34 on 700x28 tyres.
One wheel turn per pedal turn. A 50x11 is 4.55. It ignores the wheel, so it only compares gears on the same bike.
How far the bike travels per pedal turn; a 50x11 moves you 9.68 m. This is the one to use when you change tyre size.
A convention from the high-wheel era that stuck; a 50x11 is 121.3. It is still the unit most older gearing charts use.
Sheldon Brown's measure, and the only one that knows your crank length: with 165 mm cranks the same gear is 2.05, so it feels a little harder on shorter cranks.
At 90 rpm. The number riders actually feel, and the one the gear list at the top of the page shows by default.
The short answer is the one most calculators avoid: it depends on your power, your weight and the steepest ramp you will ride. A rider at 3 W/kg on a 10% climb turns about 73 rpm in a 34x34, 64 rpm in a 34x30 and 60 rpm in a 34x28. At 2.5 W/kg the same 34x34 drops to 61 rpm.
At the same power, halving the cadence doubles the force on each pedal stroke. Below around 60 rpm most riders can hold that for a minute but not for twenty. The table below is the cadence in a 34x34 across gradients and power to weight, so you can see where your own line falls.
| Gradient | 2 W/kg | 2.5 W/kg | 3 W/kg | 3.5 W/kg | 4 W/kg |
|---|---|---|---|---|---|
| 6% | 78 | 96 | 113 | 129 | 144 |
| 8% | 60 | 75 | 89 | 102 | 116 |
| 10% | 49 | 61 | 73 | 84 | 96 |
| 12% | 41 | 51 | 61 | 71 | 81 |
| 15% | 33 | 42 | 50 | 58 | 66 |
| 20% | 25 | 32 | 38 | 44 | 51 |
Cadence in rpm in a 34x34 on 700x28 tyres, for a 75 kg rider on an 8 kg bike, from the model on this page. On gradients of 10% and more, riders from 60 to 90 kg at the same W/kg land within a few rpm of these figures. Shaded cells are under 60 rpm.
The chainset sets the range, the cassette fills it in. What matters when choosing is the easiest gear, because that is the one you cannot do without on a climb, and the size of the jumps, because that is what you feel on the flat.
Each bar runs from the easiest to the hardest gear, as speed at 90 rpm, on 700x28 tyres for the double chainsets and 700x40 for 1x. Range is the hardest gear divided by the easiest, the way SRAM and Shimano quote it: a 10-52 cassette is 520%.
Four things decide it, and all four are published by the manufacturer. The calculator checks them against Shimano, SRAM and Campagnolo documents, and says so when a combination is not in any of them.
Every derailleur is specified for a minimum and maximum largest cog. Shimano Dura-Ace and Ultegra 12-speed derailleurs take an 11-30 or 11-34, not an 11-36. The 105 and GRX 12-speed derailleurs take an 11-34 or 11-36, not an 11-30. Going over the maximum is the common mistake; going under the minimum is outside the specification too.
Shimano road front derailleurs handle 16 teeth between the rings, GRX handles 17, and SRAM AXS road uses a fixed 13-tooth gap on every pair. A 50/34 is 16, so it works on Shimano and not on a SRAM 2x.
Shimano 12-speed road cassettes fit both the 12-speed HG L2 body and the older 11-speed HG L body. SRAM road cassettes with a 10-tooth cog need XDR. Campagnolo 13-speed needs N3W. A cassette on the wrong body does not go on at all.
A 12-speed cassette needs 12-speed shifting and a 12-speed chain. Shimano treats some groups as closed systems even at the same speed count: Tiagra R4000 is listed as an exception to 11-speed road interchangeability, and 12-speed mechanical and Di2 are separate boxes in its chart.
What the calculator does not check: shifter and lever pairings, frame clearance for large cogs, and brake or wheel standards. It checks the drivetrain.
| Shimano groupset | Speeds | Largest cog | Chainrings | Freehub |
|---|---|---|---|---|
| Road | ||||
| Dura-Ace R9200 Di2 (12-speed) | 12 | 30-34T | 46/36, 50/34, 52/36, 54/40 | Shimano HG L2 (12-speed road) or HG L (11-speed road) |
| Ultegra R8100 Di2 (12-speed) | 12 | 30-34T | 46/36, 50/34, 52/36 | Shimano HG L2 (12-speed road) or HG L (11-speed road) |
| 105 Di2 R7150 (12-speed) | 12 | 34-36T | 50/34, 52/36 | Shimano HG L2 (12-speed road) or HG L (11-speed road) |
| 105 R7100 mechanical (12-speed) | 12 | 34-36T | 50/34, 52/36 | Shimano HG L2 (12-speed road) or HG L (11-speed road) |
| Ultegra R8000 (11-speed) previous generation | 11 | 25-30T (2x), 28-34T (2x) | 46/36, 50/34, 52/36, 53/39 | Shimano HG L (11-speed road); Shimano HG M, or HG L with a 1.85 mm spacer |
| Ultegra Di2 R8050 (11-speed) previous generation | 11 | 25-30T (2x), 28-34T (2x) | 46/36, 50/34, 52/36, 53/39 | Shimano HG L (11-speed road); Shimano HG M, or HG L with a 1.85 mm spacer |
| 105 R7000 (11-speed) previous generation | 11 | 25-30T (2x), 28-34T (2x) | 50/34, 52/36, 53/39 | Shimano HG L (11-speed road); Shimano HG M, or HG L with a 1.85 mm spacer |
| Tiagra R4000 (11-speed, 2026) | 11 | 36T | 50/34, 52/36 | Shimano HG M, or HG L with a 1.85 mm spacer |
| Tiagra 4700 (10-speed) | 10 | 25-28T (2x), 28-34T (2x) | 48/34, 50/34, 52/36 | Shimano HG M, or HG L with a 1.85 mm spacer |
| Sora R3000 (9-speed) | 9 | 25-32T (2x), 28-34T (2x) | 50/34 | Shimano HG M, or HG L with a 1.85 mm spacer |
| Claris R2000 (8-speed) | 8 | 25-32T (2x), 28-34T (2x) | 46/34, 50/34 | Shimano HG M, or HG L with a 1.85 mm spacer |
| Gravel | ||||
| GRX RX820 mechanical (12-speed) | 12 | 34-36T (2x), 45T (1x), 51T (1x) | 48/31; 1x 40-46T | Shimano HG L2 (12-speed road) or HG L (11-speed road); Shimano Micro Spline |
| GRX RX825 Di2 (12-speed) | 12 | 34-36T (2x), 51T (1x) | 46/30, 48/31; 1x 38-46T | Shimano HG L2 (12-speed road) or HG L (11-speed road); Shimano Micro Spline |
| GRX RX610 mechanical (12-speed) | 12 | 34-36T (2x), 45T (1x), 51T (1x) | 46/30; 1x 38-40T | Shimano HG L2 (12-speed road) or HG L (11-speed road); Shimano Micro Spline |
| GRX RX717 Di2 1x (12-speed) | 12 | 51T | not listed | Shimano Micro Spline |
| GRX RX810 mechanical (11-speed) previous generation | 11 | 30-34T (2x), 40-42T (1x) | 46/30, 48/31; 1x 40-42T | Shimano HG L (11-speed road); Shimano HG M, or HG L with a 1.85 mm spacer |
| GRX RX815 Di2 (11-speed) previous generation | 11 | 30-34T (2x), 40-42T (1x) | 46/30, 48/31; 1x 40-42T | Shimano HG L (11-speed road); Shimano HG M, or HG L with a 1.85 mm spacer |
| GRX RX400 (10-speed) | 10 | 32-36T | 46/30 | Shimano HG M, or HG L with a 1.85 mm spacer |
| SRAM groupset | Speeds | Largest cog | Chainrings | Freehub |
|---|---|---|---|---|
| Road | ||||
| RED AXS E1 (2024) | 12 | 28-36T | 46/33, 48/35, 50/37, 52/39, 54/41, 56/43; 1x 38-52T | SRAM XDR |
| RED eTap AXS D1 (2019) previous generation | 12 | 26-33T (1x/2x), 28-36T (1x/2x) | 46/33, 48/35, 50/37, 52/39, 54/41 | SRAM XDR |
| Force AXS E1 (2025) | 12 | 28-36T | 46/33, 48/35, 50/37; 1x 38-50T | SRAM XDR |
| Force eTap AXS D1/D2 previous generation | 12 | 28-36T (1x/2x), 26-33T (2x) | 43/30, 46/33, 48/35, 50/37; 1x 36-50T | SRAM XDR |
| Rival AXS E1 (2025) | 12 | 28-36T | 46/33, 48/35; 1x 38-46T | SRAM XDR |
| Rival eTap AXS D1 (2021) previous generation | 12 | 28-36T | 43/30, 46/33, 48/35; 1x 38-46T | SRAM XDR |
| Gravel | ||||
| RED XPLR AXS (13-speed) | 13 | 46T | 1x 38-52T | SRAM XDR |
| RED XPLR eTap AXS (12-speed) previous generation | 12 | 36-44T | 1x 38-50T | SRAM XDR; HG 11-speed road |
| Force XPLR AXS (13-speed) | 13 | 46T | 1x 38-50T | SRAM XDR |
| Force XPLR eTap AXS (12-speed) previous generation | 12 | 36-44T | 1x 36-50T | SRAM XDR; HG 11-speed road |
| Rival XPLR AXS (13-speed) | 13 | 46T | 1x 38-46T | SRAM XDR |
| Rival XPLR eTap AXS (12-speed) previous generation | 12 | 36-44T | 1x 38-46T | SRAM XDR; HG 11-speed road |
| Apex XPLR AXS (12-speed) | 12 | 36-44T | 1x 38-42T | SRAM XDR; HG 11-speed road |
| Apex XPLR mechanical (12-speed) | 12 | 44T | 1x 38-42T | SRAM XDR; HG 11-speed road |
| Apex Eagle mechanical (12-speed) | 12 | 50-52T | 1x 38-42T | SRAM XD, or XDR with a 1.85 mm spacer; HG (8 to 10-speed length), or 11-speed road HG with a 1.85 mm spacer |
| Campagnolo groupset | Speeds | Largest cog | Chainrings | Freehub |
|---|---|---|---|---|
| Road | ||||
| Super Record 13 (2x13) | 13 | 36T | 45/29, 48/32, 50/34, 52/36, 53/39, 54/39, 55/39 | Campagnolo N3W |
| Record 13 (2x13) | 13 | 36T | 45/29, 48/32, 50/34, 52/36, 53/39, 54/39, 55/39 | Campagnolo N3W |
| Super Record 1x13 Road | 13 | 36T (1x), 48T (1x) | 1x 44-52T | Campagnolo N3W |
| Record 1x13 Road | 13 | 36T (1x), 48T (1x) | 1x 44-52T | Campagnolo N3W |
| Super Record S Wireless (12-speed) | 12 | 32T | 45/29, 48/32, 50/34, 52/36, 53/39, 54/39 | see manufacturer |
| Super Record Wireless (12-speed, 2022) previous generation | 12 | 32T | 45/29, 48/32, 50/34, 52/36 | see manufacturer |
| Super Record 12 mechanical | 12 | 34T | 50/34, 52/36, 53/39 | Campagnolo freehub, or N3W with the Campagnolo adapter |
| Chorus 12 | 12 | 34T | 48/32, 50/34, 52/36 | Campagnolo freehub, or N3W with the Campagnolo adapter |
| Gravel | ||||
| Super Record 13 All Road (2x13) | 13 | 36T | 45/29, 48/32, 50/34, 52/36, 53/39, 54/39, 55/39 | Campagnolo N3W |
| Record 13 All Road (2x13) | 13 | 36T | 45/29, 48/32, 50/34, 52/36, 53/39, 54/39, 55/39 | Campagnolo N3W |
| Super Record X (1x13) | 13 | 48T | 1x 38-52T | Campagnolo N3W |
| Record X (1x13) | 13 | 48T | 1x 38-52T | Campagnolo N3W |
| Ekar (1x13) | 13 | 44T | 1x 38-44T | Campagnolo N3W |
| Ekar GT (1x13) | 13 | 48T | 1x 36-44T | Campagnolo N3W |
From the rear derailleur specifications in each manufacturer's documents. Ring pairs are the ones the manufacturer lists for the groupset.
The reliable way to size a chain is on the bike: wrap it around the largest chainring and the largest cog without going through the rear derailleur, then add one inch, which is two links. That is Park Tool's method, and Sheldon Brown describes the same one. The estimate below does the same thing on paper, so you know what to buy before the bike is in the stand.
Measure from the centre of the bottom bracket to the centre of the rear axle. The ring and cog follow setup A until you change them.
With a half-inch chain pitch, the chain wraps half the chainring (its teeth divided by four, in inches), half the cog (the same), and runs twice the length of the chainstay between them. Add the one inch of slack and round up to a whole inch, because links come in pairs.
Example: a 410 mm chainstay with a 50T ring and a 34T cog gives 55 inches, which is 110 links.
Park Tool adds a second inch for cogs of 42T and larger; the calculator adds it above 36T. SRAM 1x systems and Campagnolo 13-speed publish their own sizing procedures, and on a full-suspension bike the chain must be sized with the suspension compressed. Confirm on the bike before you cut.
Hardknott is the climb that decides the Fred Whitton: 13.3% on average and 33% at its steepest, according to the organisers' climbs guide. Take a 75 kg rider holding 225 W, which is 3 W/kg, on an 8 kg bike with 700x28 tyres.
On the average gradient, a compact with an 11-28 leaves them at 46 rpm and an 11-34 at 56 rpm. On the 33% ramp the speed falls to 3.1 km/h and the cadence to 20 rpm in a 34x28, 24 rpm in a 34x34 and 25 rpm in a 34x36.
The conclusion is not that a 36T cog makes Hardknott easy; nothing does at 33%. It is that the 11-28 turns the average gradient into a grind before the ramps even start, and that the difference between a 34 and a 36 cog is small next to the difference between 34 and 28.
Said plainly, because each one is a way these numbers get misread.
The rollout comes from the rim standard and the tyre width, and a real tyre on a real rim can be 1 to 2 percent off. If you have measured your rollout, enter it and every number updates.
Its rolling resistance is the value measured for high-pressure tyres on smooth asphalt. On gravel you need an easier gear than it says, and we have not found a peer-reviewed rolling-resistance figure for gravel to model it properly.
The power you can hold falls as a climb gets longer and as the day goes on. The model takes the power you give it; choosing an honest number is your part.
It checks derailleur range, ring difference, freehub and chain against manufacturer documents. It does not check levers, frame clearance or anything a manufacturer has not published. When a combination is not in any chart, it says so instead of guessing.
The power model is peer reviewed. The definitions are standard. Every compatibility figure comes from the manufacturer that makes the part.
Divide the chainring teeth by the cog teeth. A 50-tooth ring with an 11-tooth cog is 4.55, and a 34 with a 34 is 1.00. To make it useful across bikes, multiply by the wheel circumference to get development in metres, or by the wheel diameter to get gear inches. The calculator does all three for every combination at once.
One that keeps you above about 60 rpm on the steepest ramp you will ride. At 3 W/kg, a 34x34 turns about 73 rpm on a 10% gradient; at 2.5 W/kg it is 61 rpm, only just above that line. So below 3 W/kg, on climbs that stay over 10%, your easiest gear should be 1.0 or lower, which on a compact chainset means a 34T largest cog or bigger.
Gear ratio is teeth divided by teeth and ignores the wheel. Gear inches multiply it by the wheel diameter, development multiplies it by the wheel circumference in metres. Gear inches and development compare bikes with different wheels; the ratio only compares gears on the same bike.
They are calculated from the rim standard and the nominal tyre width, which lands within 1 to 2 percent of a measured wheel. That is enough to compare gears. For exact speeds, roll the bike one full wheel turn, measure the distance in millimetres and enter it as your rollout.
Each pedal stroke is easier, yes, and you cover less ground with it. The work to get up a climb is the same in any gear; a lower ratio lets you do it at a higher cadence and a lower force per stroke, which most riders can sustain for longer.
It tells you whether it fits your drivetrain as the manufacturer documents it: the rear derailleur range, the front derailleur ring difference, the freehub body and the chain, for 47 Shimano, SRAM and Campagnolo groupsets. It does not check frame clearance or levers, and when you mix brands it says no chart covers it.
Not within Shimano's specifications. The Ultegra R8100 and Dura-Ace R9200 rear derailleurs take an 11-30 or an 11-34. The 11-36 is specified for the 105 and GRX 12-speed derailleurs, which in turn do not take an 11-30.
Twice the chainstay length plus a quarter of the teeth on the largest ring and the largest cog, plus one inch, all in inches and rounded up; double it for links. A 410 mm chainstay with 50T and 34T gives 110 links. Always confirm on the bike with the largest ring and largest cog before cutting.
