Belt Transmissions - Speed and Length of Belts

Belts (or chains) are used to transfer power through rotational motion from one shaft to another. This tool calculates belt length, velocity, gearing ratios, horsepower, and speed ratios for belt transmission systems used in HVAC and other mechanical applications.

Belt Transmissions - Speed and Length of Belts

Belts (or chains) are used to transfer power (or convert torque) through rotational motion from one shaft to an other. Belt driven fans are common in heating, ventilation, air-conditioning and cooling (HVAC) systems.

Calculator Inputs

Enter the parameters for your belt transmission system below.

Calculator

Inputs

Pulley Diameter - Motor (mm)

Pulley Diameter - Fan (mm)

Center to Center Distance (mm)

Motor Speed (rpm)

Belt Tension (lbf)

Torque (ft-lbf)

Results

Belt Length-- mm

Belt Velocity-- m/s

Follower Speed (Fan)-- rpm

Power (from tension)-- hp

Power (from torque)-- hp

Speed Ratio-- ratio

Pitch Diameter of Pulley (in)	850 rpm	1050 rpm	1075 rpm	1140 rpm	1550 rpm	1725 rpm	3450 rpm
1	223	275	281	298	406	452	903
2	445	550	563	597	812	903	1806
3	668	825	844	895	1217	1355	2710
4	890	1100	1126	1194	1623	1806	3613
5	1113	1374	1407	1492	2029	2258	4516
6	1335	1649	1689	1791	2435	2710	5419
7	1558	1924	1970	2089	2841	3161	6322
8	1780	2199	2251	2388	3246	3613	7226
9	2003	2474	2533	2686	3652	4064	8129
10	2225	2749	2814	2985	4058	4516	9032

Formulas Used

Belt Length

lb = (dm × π / 2) + (df × π / 2) + (2 × lfm) + ((df - dm)² / (4 × lfm))

Belt Velocity

vb = π × dm × nm / 60000 (metric units, m/s)

Belt Gearing

nf = nm × dm / df

Horsepower

From Tension: Php = Fb × vb / 33000

From Torque: Php = T × n / 5252

Speed Ratio

SR = nf / ns (where nf is faster and ns is slower)