This calculator models a two-pulley belt drive with no slip in its speed ratio and a user-entered aggregate efficiency applied to transmitted power. It does not select a belt or establish a safe power rating.
Belt Drive Power Transmission Interactive Calculator
Enter driver speed and torque, effective driver and driven pulley diameters, and an assumed aggregate efficiency. Results are arithmetic estimates, not a belt-drive rating.
Equation Used
- The driver is the pulley with entered diameter D1 and the driven pulley has entered diameter D2.
- Both diameter inputs are compatible effective pitch or datum diameters.
- The belt has no slip or creep for the displayed speed ratio.
- Entered aggregate efficiency is applied once to transmitted power.
- Belt type, section, width, count, tension, wrap, centre distance, load spectrum, service factor, shaft load and safe design are omitted.
Two Pulleys Coupled by One Belt
Belt-drive design manuals define drive ratio using compatible pitch or datum diameters and driver/driven speeds. With no slip, belt linear speed is the same at both pulleys, so N1D1=N2D2.
This calculator applies a separate user-entered efficiency to power after the ideal speed ratio. It does not infer that efficiency from pulley or belt geometry.
What This Calculator Does
The tool uses input power from torque and angular speed to calculate delivered power under the entered efficiency. Its four outputs show effective diameter ratio, no-slip driven speed, driven torque and assumed aggregate power loss.
It does not select a belt, pulley, tension, centre distance, shaft or guard.
Ideal Ratio and Assumed Power Balance
N2 = N1/i
Pin = T1(2 pi N1/60)
Pout = eta Pin
T2 = Pout/(2 pi N2/60)
Ploss = Pin-Pout
Power is converted to kW by dividing watts by 1000.
Worked Arithmetic Example
For 1485 rpm, 1286 N*m, D1=80 mm, D2=330 mm and eta=94%, the effective diameter ratio is 4.125:1, no-slip driven speed is 360 rpm, assumed driven torque is about 4986 N*m and assumed aggregate loss is about 12.0 kW.
Model Boundary
- Mechanical arrangement: belt-drive ratio uses compatible effective pulley diameters and driver/driven speed.
- Calculated: ideal no-slip ratio plus a user-assumed single efficiency power balance.
- Not calculated: slip, creep, belt section, pitch, teeth, groove geometry, width, belt count, centre distance, wrap angle, installation tension, dynamic tension, centrifugal effects, shaft load, bearing load, service factor, shock, starts, duty cycle, resonance, alignment, wear, temperature, contamination, belt rating, pulley strength, shaft strength, guarding or safe design.
Frequently Asked Questions
Which pulley is the driver?
D1 is the entered driver pulley and D2 is the driven pulley, regardless of which is larger.
Can the ratio be below 1?
Yes. If D2 is smaller than D1, the ideal driven speed increases.
Should I enter outside diameter?
Only if it is the specified effective diameter for that belt system. Use compatible pitch or datum diameters.
Does efficiency change the speed ratio?
Not in this model. It reduces delivered power and torque; slip is excluded.
Does the calculator rate a belt?
No.
Can it determine installation tension or shaft load?
No. Those require belt-specific design data and complete geometry.
References
- Gates, Industrial Timing Belt Design Manual: i=r/R=N/n=D/d and definitions for pitch diameter, pulley speed, belt speed and transmitted power.
- Optibelt, Technical Manual V-Belt Drives: datum-diameter terminology, driver/driven pulley symbols, drive ratio, speed, belt tension, wrap and design variables.
- Gates, Heavy Duty V-Belt Drive Design Manual: drive selection requires application, power, speed or ratio, centre distance, contact arc and tension considerations.
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