How do you calculate sprocket ratio?

Divide the driven sprocket’s teeth by the driver’s teeth. A 36-tooth sprocket driven by an 18-tooth sprocket is 36 ÷ 18 = 2:1.

How do I calculate output rpm from a sprocket ratio?

Divide input rpm by the ratio, or multiply it by driver teeth ÷ driven teeth. 300 rpm through 18 to 36 teeth gives 150 rpm.

Does chain size change the ratio?

No. Ratio depends only on tooth counts. Chain size changes sprocket diameter and chain speed: the same 18-tooth sprocket at 300 rpm moves #40 chain at 225 ft/min and #60 chain at 337.5 ft/min.

How does sprocket ratio affect torque?

Torque rises by the ratio, less chain losses. A 2:1 reduction turns 10 N·m into about 19 to 20 N·m at a typical 95 to 98% chain efficiency.

Is this a motorcycle sprocket calculator?

It uses the same ratio math (rear teeth ÷ front teeth, so 15 and 45 teeth give 3.0:1), but it does not model gearbox ratios, tire size, or road speed. It designs industrial roller chain sprockets and their ratio and chain speed.

What is the largest ratio for one chain stage?

Single chain stages commonly stay at about 6:1 or less, because high ratios shrink wrap on the small sprocket and need a very large driven sprocket. Use two stages for larger reductions, or check the gear ratio calculator for compound trains.

Power transmission calculator

Sprocket Ratio & Speed Calculator

Calculate sprocket gear ratio, output rpm, and chain speed from driver and driven tooth counts, then generate either sprocket for laser cutting.

Build a laser-cut plate sprocket

Select a roller chain and tooth count, then set the bore, holes, and plate.

Units

Roller chain

Sprocket teeth

Shaft speed

rpm

Chain pitch

Roller diameter

Tooth fit

Mating sprocket

Add the driven sprocket to see the ratio and output speed, and generate both parts.

Hub, holes, and plate

Bore

Bore diameter

Mounting holes

Lightening holes

Fabworks plate material

Plate thickness for chain fitMin. feature 0.050 in · 1.27 mm

Generated dimensions

Recommended chain fit

Pitch diameter: 2.8794 in
Outside diameter: 3.1356 in
Root diameter: 2.5628 in
Roller seat radius: 0.1583 in
Chain speed At 300 rpm: 225 ft/min
Plate: Steel 1008 · 0.187 in
Chain side clearance: 0.0628 in per side

ANSI roller chain dimensions

Recommended plate thickness leaves side clearance inside the chain.

ANSI #40 selected

Chain	Pitch	Roller diameter	Inside width	Ideal plate
ANSI #25	0.250 in · 6.35 mm	0.130 in · 3.302 mm	0.125 in · 3.175 mm	0.098 in · 2.5 mm
ANSI #35	0.375 in · 9.525 mm	0.200 in · 5.08 mm	0.188 in · 4.763 mm	0.118 in · 3 mm
ANSI #40	0.500 in · 12.7 mm	0.312 in · 7.925 mm	0.313 in · 7.938 mm	0.250 in · 6.35 mm
ANSI #41	0.500 in · 12.7 mm	0.306 in · 7.772 mm	0.250 in · 6.35 mm	0.188 in · 4.763 mm
ANSI #50	0.625 in · 15.875 mm	0.400 in · 10.16 mm	0.375 in · 9.525 mm	0.313 in · 7.938 mm
ANSI #60	0.750 in · 19.05 mm	0.469 in · 11.913 mm	0.500 in · 12.7 mm	0.375 in · 9.525 mm

Laser-cut profile preview

The B29.1 profile uses a roller seating curve, working curve, tangent flat, and topping curve. The dashed circle is the pitch circle and the filled circle is a seated roller.

ASME B29.1 profile

Download the manufacturing files

100% in-browser

STEP solids are built and checked in your browser. DXF and SVG drawings use lines and true arcs at full scale. Nothing is uploaded until you order.

Sprocket
3.136 in × 3.096 in

Laser cut it at Fabworks

We generate the STEP files, add them to a new quote, and open it in a new tab where you can review material, finish, and quantity.

The STEP uses the ASME B29.1 theoretical tooth form and catalog outside-diameter truncation. Manufacturing tolerances, material, heat treatment, alignment, lubrication, and application loads still require engineering review.

Quick answer

How this sprocket ratio calculator works

Sprocket ratio is driven teeth ÷ driver teeth: an 18-tooth sprocket driving a 36-tooth sprocket is 2:1, so 300 rpm in gives 150 rpm out and about twice the torque before losses. Enter both tooth counts and the input speed to get ratio, output rpm, and chain speed, with the sprocket profile ready to download or order.

How to use the calculator

1Choose the chain size so chain speed uses the right pitch.
2Enter the driver sprocket teeth and the input shaft speed in rpm.
3Enter the mating (driven) sprocket teeth.
4Read the ratio, output speed, and chain speed, then link to the chain length calculator for the center distance.
5Generate either sprocket and download STEP, DXF, or SVG, or send it to a Fabworks quote.

Key formulas

Sprocket ratio formulas

Sprocket ratio: i = N_driven ÷ N_driver; Tooth counts of the driven and driver sprockets.
Output speed: n_out = n_in × N_driver ÷ N_driven; Speeds in rpm.
Output torque, ideal: T_out = T_in × i × η; η is drive efficiency; roller chain drives commonly run around 95 to 98%.
Chain speed: v = N × p × n ÷ 12 (ft/min); Use either sprocket’s teeth and speed; p in inches. Metric: v = N·p·n ÷ 1000 m/min with p in mm.

Worked example

18 teeth driving 36 teeth at 300 rpm

Inputs: #40 chain (p = 0.500 in), 18-tooth driver at 300 rpm, 36-tooth driven sprocket.
Result: Ratio 2:1, output 150 rpm, chain speed 225 ft/min (68.6 m/min).

Ratio = 36 ÷ 18. Output = 300 × 18 ÷ 36. Chain speed = 18 × 0.500 in × 300 rpm ÷ 12 = 225 ft/min.

Common questions

What to know before using the result

How do you calculate sprocket ratio?: Divide the driven sprocket’s teeth by the driver’s teeth. A 36-tooth sprocket driven by an 18-tooth sprocket is 36 ÷ 18 = 2:1.
How do I calculate output rpm from a sprocket ratio?: Divide input rpm by the ratio, or multiply it by driver teeth ÷ driven teeth. 300 rpm through 18 to 36 teeth gives 150 rpm.
Does chain size change the ratio?: No. Ratio depends only on tooth counts. Chain size changes sprocket diameter and chain speed: the same 18-tooth sprocket at 300 rpm moves #40 chain at 225 ft/min and #60 chain at 337.5 ft/min.
How does sprocket ratio affect torque?: Torque rises by the ratio, less chain losses. A 2:1 reduction turns 10 N·m into about 19 to 20 N·m at a typical 95 to 98% chain efficiency.
Is this a motorcycle sprocket calculator?: It uses the same ratio math (rear teeth ÷ front teeth, so 15 and 45 teeth give 3.0:1), but it does not model gearbox ratios, tire size, or road speed. It designs industrial roller chain sprockets and their ratio and chain speed.
What is the largest ratio for one chain stage?: Single chain stages commonly stay at about 6:1 or less, because high ratios shrink wrap on the small sprocket and need a very large driven sprocket. Use two stages for larger reductions, or check the gear ratio calculator for compound trains.

Reference

Common sprocket ratios at 300 rpm input, #40 chain

Driver teeth	Driven teeth	Ratio	Output rpm	Chain speed (ft/min)
12	24	2.00:1	150	150
12	36	3.00:1	100	150
15	30	2.00:1	150	187.5
15	45	3.00:1	100	187.5
18	36	2.00:1	150	225
18	54	3.00:1	100	225
20	60	3.00:1	100	250
24	48	2.00:1	150	300

Formula

Dₚ = p ÷ sin(180° ÷ N)

Pitch diameter Dₚ is set by chain pitch p and tooth count N. The generated profile follows the ASME B29.1-2011 (R2022) theoretical tooth construction: roller seating curve, working curve, tangent flat, topping curve, and catalog outside-diameter truncation.

Engineering references

Assumptions and limits

Presets use nominal ANSI roller-chain pitch and roller diameter values covered by ASME B29.1.
The browser-generated STEP is a closed, uniform-thickness plate sprocket with a round bore.
Nominal fit uses the standard theoretical minimum seating curve; optional clearance and tip relief are deliberate deviations for prototype tuning.
Hubs, keyways, bore tolerances, material, heat treatment, and high-speed applications require an engineering review.
Chain speed assumes the sprocket rotates at the entered shaft speed without slip.

Educational estimate

Use this result for learning and early design exploration. Verify safety-critical or production decisions with the governing standard, material data, real tooling, and a qualified engineer.

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