Pulley RPM & Speed Ratio Calculator
Calculate driven RPM, speed ratio, and belt speed
Driver pulley से driven pulley ki RPM और belt speed निकालें
Pulley RPM and speed ratio follow one rule: belt speed at both pulleys is identical, so N_driver × D_driver = N_driven × D_driven, where N is RPM and D is pitch diameter. Rearranged: driven RPM = driver RPM × (driver Ø / driven Ø). A 100 mm motor pulley spinning at 1440 RPM driving a 300 mm pulley gives 1440 × (100/300) = 480 RPM at the output — a 3:1 speed reduction with a matching 3× torque gain. Belt linear speed is v = π × D × N / 60 in m/s (with D in metres). For typical industrial drives, keep belt speed below 25 m/s for classical V-belts (A, B, C) and 35 m/s for narrow sections (SPZ, SPA, SPB). This calculator returns driven RPM, speed ratio, and belt speed — the three numbers you need when sizing a compressor, pump, grinder, or conveyor drive.
Calculator
Motor side
Load side
4-pole: 1440 · 2-pole: 2880 · 6-pole: 960
Formulas: N_driven = 1440 × (100 / 300) = 480 RPM. Belt speed v = π × D_driver × N / 60000 = 7.54 m/s. Torque at driven shaft ≈ 3.00× driver torque (minus belt losses).
ƒFormula
N_driven = N_driver × (D_driver / D_driven) | v_belt = π × D × N / 60 (m/s)N is pulley RPM; D is pulley pitch diameter. Since the belt doesn't stretch, linear speed at both pulleys is identical: N × D is a constant. Rearranging gives the output RPM formula. Belt linear speed v uses D in metres and N in RPM, result in m/s. Maximum safe belt speed: 25 m/s for A/B/C classical, 35 m/s for SPZ/SPA/SPB narrow.
Units: RPM: revolutions per minute · D: millimetre (or metre for v calculation)
Pulley RPM calculation kaise karein?
Pulley drive mein ek basic rule hai, belt ki speed dono pulleys pe same rehti hai. Iska matlab: N_driver × D_driver = N_driven × D_driven. Yaani: agar motor pulley chhota hai aur driven pulley bada, toh driven pulley slow chalegi (speed reduction). Agar ulta hai, toh speed badh jayegi. Formula: driven RPM = motor RPM × (motor pulley Ø / driven pulley Ø). Belt ki linear speed v = π × D × N / 60 m/s. Zyada speed (above 25 m/s) se classical V-belts pe slip aur heating hoti hai.
Worked Examples
Sizing a water pump drive
Problem: A 3 HP motor at 1440 RPM drives a water pump that needs 720 RPM. Motor pulley 100 mm, what driven pulley?
Solution: Need 2:1 reduction: driven Ø = 100 × (1440/720) = 200 mm. Use a 200 mm pulley on the pump. Speed ratio 2:1 means output torque is 2× the motor torque (minus belt losses).
Step-up drive for a high-speed grinder
Problem: A 1440 RPM motor drives a grinder requiring 3600 RPM. Motor pulley 200 mm — driven pulley?
Solution: Need 1:2.5 step-up: driven Ø = 200 × (1440/3600) = 80 mm. Belt speed on motor pulley = π × 0.2 × 1440/60 = 15.1 m/s, still safe. But verify the small pulley (80 mm) is at least 3× the belt section thickness to avoid fatigue.
Belt speed check for high-speed compressor
Problem: Motor 2880 RPM, pulley 150 mm. Is belt speed safe for A-section?
Solution: v = π × 0.15 × 2880 / 60 = 22.6 m/s. Below the 25 m/s classical V-belt limit — safe. For peace of mind, switch to SPA narrow section which handles up to 35 m/s.
Common Motor RPM & Pulley Ratios, Quick Reference
| Motor RPM | Motor Pulley Ø | Ratio → Driven RPM | Belt Speed (m/s) |
|---|---|---|---|
| 1440 (4-pole) | 80 mm | 1:1 → 1440 | 6.0 |
| 1440 | 100 mm | 1:2 → 720 | 7.5 |
| 1440 | 100 mm | 1:3 → 480 | 7.5 |
| 1440 | 150 mm | 1:2 → 720 | 11.3 |
| 1440 | 200 mm | 2:1 step-up → 2880 | 15.1 |
| 2880 (2-pole) | 100 mm | 1:1 → 2880 | 15.1 |
| 2880 | 150 mm | 1:2 → 1440 | 22.6 |
| 2880 | 200 mm | 1:3 → 960 | 30.2 ⚠️ narrow only |
| 960 (6-pole) | 100 mm | 1:1 → 960 | 5.0 |
| 960 | 150 mm | 1:2 → 480 | 7.5 |
Indian 50 Hz motors: 2-pole = 2880 RPM, 4-pole = 1440 RPM, 6-pole = 960 RPM, 8-pole = 720 RPM. Minimum recommended small pulley Ø: ≥ 3× belt thickness for classical, ≥ 2× for narrow sections.
Need the actual parts? We stock them in Noida.
Shri Narayan Machinery LLP · C-101, Sector 9, Noida · Call +91-9811104037 · GST invoice on every order
Endura V-Belts
Classical (A/B/C), narrow (SPZ/SPA/SPB/SPC), and cogged belts in all sizes.
View productsSKF Bearings
Pillow blocks and deep-groove bearings for motor and driven shaft support.
View productsIndustrial Supplies
V-pulleys, taper-lock bushings, belt tensioners, and drive accessories.
View productsFrequently Asked Questions: Pulley RPM & Speed Ratio Calculator
Related Calculators
V-Belt Length Calculator
Enter small pulley Ø, big pulley Ø, and center distance. Get belt length in mm and inches. Supports A, B, C, D, Z, SPZ, SPA, and SPB sections.
Bearing Number Decoder
Decode any ISO / SKF bearing designation into its physical dimensions and type. 6205 → bore 25, OD 52, width 15 mm.
Need Help Picking the Right Product?
Our team at Shri Narayan Machinery has been supplying industrial parts in Noida for years. Tell us what you're building and we'll recommend the right cylinder, bearing, bolt, belt, or drill.