Shaft Torque & Coupling Size Calculator
Work out shaft torque from horsepower and speed, then size a Reuland / Trilex RC jaw coupling with the right service factor, bore and insert. Formulas shown below.
How these are calculated
| Result | Formula |
|---|---|
| Shaft torque | T (lb-in) = 63,025 × HP ÷ RPM (lb-ft = lb-in ÷ 12; N·m = lb-in × 0.11298) |
| Design torque | T design = shaft torque × service factor |
| Coupling size | smallest RC size whose rated torque (with the chosen insert) ≥ design torque, and whose bore range takes both shafts |
RC coupling ratings used
| Size | Bore range (in) | Rated torque, L9 (lb-in) | Rated torque, H5 (lb-in) |
|---|---|---|---|
| RC1 | 0.375 – 1.125 | 473 | 630 |
| RC2 | 0.375 – 1.375 | 630 | 1,103 |
| RC3 | 0.500 – 1.625 | 1,261 | 2,206 |
| RC4 | 0.625 – 1.875 | 1,576 | 3,309 |
| RC5 | 0.750 – 2.375 | 3,466 | 6,933 |
| RC6 | 0.750 – 2.625 | 7,563 | 15,756 |
| RC7 | 1.125 – 2.875 | 12,605 | 28,361 |
| RC8 | 1.250 – 3.875 | 31,513 | 47,269 |
Service factors used
| Load | Electric motor or turbine | Engine, 6+ cylinders | Engine, under 6 cylinders |
|---|---|---|---|
| Light | 1.0 | 1.5 | 2.0 |
| Moderate | 1.5 | 2.0 | 2.5 |
| Heavy | 2.0 | 2.5 | 3.0 |
Ratings, bore ranges, service factors and insert guidance are from Reuland and Trilex RC coupling data, the same figures as our Reuland / Trilex couplings page. The 63,025 constant is the standard horsepower-torque conversion; Reuland's selection guide rounds it to 63,000. Results are estimates for sizing: confirm against the manufacturer's data, or send us your numbers.
Frequently asked questions
How do you calculate torque from horsepower and RPM?
Torque in pound-inches equals 63,025 times horsepower divided by RPM. A 10 HP motor at 1,750 RPM produces about 360 lb-in, or 30 lb-ft. In metric units, torque in newton-metres equals 9,549 times kilowatts divided by RPM.
What is a coupling service factor?
A multiplier for shock and uneven load. With an electric motor, use 1.0 for light, steady loads such as fans and centrifugal pumps, 1.5 for moderate shock such as elevators and mixers, and 2.0 for heavy shock such as crushers. Engines raise the factor by 0.5 to 1.0. Multiply the shaft torque by it to get the design torque.
How do I choose the coupling size?
Choose the smallest size whose rated torque, with the insert you will use, is at or above the design torque, and whose bore range takes both shafts. If a shaft is too large for the size that covers the torque, step up to the next size.
Should I use the L9 or H5 insert?
Use the black L9 Hytrel insert for service factors up to 1.5 and the blue H5 for service factors above 1.5 or severe duty. The H5 also has a higher torque rating, so it can allow a smaller coupling. Trilex may mark the blue insert H9.
Can the two shafts be different sizes?
Yes. Each coupling half is bored separately, so an RC coupling can join, for example, a 1-3/8 inch motor shaft to a 1-1/4 inch gearbox shaft, as long as both are inside the size's bore range.
Can Jealco supply the coupling?
Yes. We stock Reuland and Trilex RC coupling halves and inserts and can quote other coupling types when the torque or shafts are outside the RC range. Send us the motor and driven shaft details.
Related
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Size, bore, keyway and torque tables.
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Need a coupling sized or bored?
Send us the motor and driven shaft details and we will confirm the size, bores and keyways, and quote the halves and insert.