Working Formulas

Code of Symbols Click to view the code of symbols used in formulas below

B Sine of Angle of Incline G2 Load per Hour (in lbs.) C Center to Center distance (in Inches)
HP Horsepower D Diameter or Drive Pulley (in inches) K Drive Factor
(See Table #2)
d Diameter of Tail Pulley (in inches) L Belt Length (in inches) E Effective Tension (in lbs.)
M Belt Weight (See weight in lbs. PIW for particular belt specification)(overall length, not center to center) E1 Slack Side Tension (in lbs.) P Product Weight (in lbs.)
E2 Tight Side Tension (in lbs.) RPM Revolutions per Minute F Coefficient of Friction
(See Table #1)
S Speed (Feet Per Minute) G1 Load Per Sq. or Cu. Ft. (in lbs.) T Operating Tension PIW (in lbs.)
W Belt Width (in inches)

Belt Length

when pulleys are approximately the same size

L = D + d x 3.1416 + 2C

Belt Length

when one pulley is much larger than the other (at least 3 or more times larger)

L = D + d x 3.1416 + 2C + (D - d)2
2 4C

Belt Speed

in Feet Per Minute

S = D x RPM x .2618 x 1.021

Load on Belt

at one time when load is known (per square foot or per cubic foot basis)

P = G1 x C (in ft.) x W (in ft.)

Load on Belt

at one time when load is known (by lbs. per hour or tons per hour)

P = G2 x C (in ft.)
S x 60 (minutes)

Belt Weight

L (in ft.) x (Belt Weight PIW x W)


to drive horizontal belt conveyors

HP = F x S x (P + M)


to drive inclined belt conveyors

HP = (P x B) + (P + M) x F x S

Effective Tension

pull needed to move belt and load horizontally

E = F x (P +M)

Slack Side Tension

additional tension required to prevent slippage on drive pulley

E1 = E x K

Tight Side Tension

total tension required to move belt and load

E2 = E + E1

Operating Tension

determines working strength of belt to handle job on per inch of width basis

T = E2

Length of Belt in a Roll

approximate only

L = D2 - 100
D Diameter in inches
T Thickness in inches
L Length in Feet

Table #1

Coefficient of Friction "F"
(Belt to Slider Bed or Rollers)

Belt Steel or Aluminum Metal Rollers
FS pulley side .30 to .35 .10 to .15
Bare Duck or BB side .20 to .25 .10 to .15
Cover on pulley side .50 to .55 .10 to .15
Note:  The highest figure is the most conservative

Table #2

Drive Factor "K"
Belt Wrap on Drive Pulley Screw Take-Up Gravity or Weighted Take-Up
Bare Lagged Bare Lagged
180° 1.6 1.0 .84 .50
220° 1.2 .6 .62 .35
240° 1.0 .5 .54 .30
Note:  The drive factor has a definite effect on tension