Engineering Formulas
Engineering Formulas

Below is a list of helpful engineering formulas


Ohm's Law:
Ohms = Volts/Amperes (R = E/I)
Amperes = Volts/Ohms (I = E/R)
Volts = Amperes x Ohms (E = IR)

Power-- A/C Circuits:
Efficiency = 746 x Output Horsepower
                  Input Watts

Three-Phase Kilowatts= Volts x Amperes x Power Factor x 1.732
                                          1000

Three-Phase Volt-Amperes = Volts x Amperes x 1.732

3-Phase Amperes =            746 x Horsepower              
                  1.732 x Volts x Efficiency x Power Factor

3-Phase Efficiency =           746 x Horsepower              
                      Volts x Amperes x Power Factor x 1.732

Three-Phase Power Factor =        Input Watts      
                           Volts x Amperes x 1.732

Single-Phase Kilowatts = Volts x Amperes x Power Factor
                                        1000

Single-Phase Amperes =          746 x Horsepower       
                       Volts x Efficiency x Power Factor

Single-Phase Efficiency =             746 x Horsepower       
                             Volts x Amperes x Power Factor

Single-Phase Power Factor =   Input Watts  
                            Volts x Amperes

Horsepower (3-phase) = Volts x Amperes x 1.732 x Efficiency x Power Factor
                                             746

Horsepower (1-phase) = Volts x Amperes x Efficiency x Power Factor
                                          746

Power - D-C Circuits:
Watts = Volts x Amperes (W = EI)

Amperes = Watts  (I = W/E)
          Volts

Horsepower = Volts x Amperes x Efficiency
                         746
Speed - A-C Machinery:
Synchronous RPM = Hertz x 120
                     Poles

Percent Slip = Synchronous RPM - Full-Load RPM  x 100
                      Synchronous RPM

 


Motor Application:
Torque (lb.-ft.) = Horsepower x 5250
                          RPM

Horsepower = Torque (lb.-ft.) x RPM
                      5250
Time for Motor to Reach Operating Speed (seconds):

Seconds =       WK2 x Speed Change      
          308 x Avg. Accelerating Torque

WK2 = Inertia of Rotor + Inertia of Load (lb.-ft.2)

Average Accelerating Torque = [(FLT + BDT)/2] + BDT + LRT
                                           3

FLT = Full-Load Torque             BDT = Breakdown Torque

LRT = Locked Rotor Torque

Load WK2 (at motor shaft) = WK2 (Load) x Load RPM2
                                  Motor RPM2
Shaft Stress (P.S.I.) =   HP x 321,000   
                        RPM x Shaft Diam.3

Centrifugal Applications:
- Affinity Laws for Centrifugal Applications

Flow1 = RPM1
Flow2   RPM2

Pres1 = (RPM1)2
Pres2   (RPM2)2

BHP1 = (RPM1)3
BHP2   (RPM2)
3
For Pumps:
BHP = GPM x FT x Specific Gravity
       3960 x Efficiency of Pump

BHP = GPM x PSI x Specific Gravity
       1713 x Efficiency of Pump

Head in Feet = 2.31 PSIG

For Fans and Blowers:
BHP =          CFM x PSF         
       33000 x Efficiency of Fan

BHP =          CFM x PSW       
       6344 x Efficiency of Fan

BHP =        CFM x PSI       
      229 x Efficiency of Fan
Where:
BHP  = Brake Horsepower
CFM  = Cubic Feet per Minute
FT   = Feet
GPM  = Gallons per minute
PSI  = Pounds per square inch
PSIG = Pounds per square inch gravity
PSF  = Pounds per square foot
PIW  = Inches of water gauge
Specific Gravity of Water = 1.0

INDUSTRY ABBREVIATIONS

cm = centimeter cu. = cubic ft. = foot gl. = gallon (US)
gr. = gram Imp. = Imperial in. = inch kg. = kilogram
km. = kilometer l. = liter lb. = pound m. = meter
mi. = mile oz. = ounce qt. = quart std. = standard
US = United States yd. = yard    

LENGTH MEASUREMENTS

    Common Usage   Reciprocal Value
    1 ft. = 12 in..   1 in. = 0.0833 ft.
    1 yd. = 3 ft.   1 ft. = 0.3333 yd.
    1 rod = 5.5000 yd.   1 yd. = 0.1818 rods
    1 furlong = 40 rods   1 rod = 0.0250 furlongs
    1 mile = 8 furlongs   1 furlong = 0.1250 mi.
    1 mi. = 5,280 ft.   1 ft. = 0.000189 mi.
    1 mi. = 1,760 yd.   1 yd. = 0.000568 mi.
    1 fathom = 6 ft.   1 ft. = 0.1667 fathom
    120 fathoms = 1 cable   1 cable = 0.00833 fathoms
    1 league = 3 mi.   1 mi. = 0.3333 leagues
    1 nautical mi. = 6076.11 ft.   1 ft. = 0.000165 natical mi.
    1 hand = 5 in. (equestrian)   1 in. = 0.2000 hands
         
METRIC
    1 in. = 2.54 cm.   1 cm. = 0.3937 in.
    1 ft. = 30.48 cm.   1 cm. = 0.0328 ft.
    1 m. = 3.2808 ft.   1 ft. = 0.3048 m.
    1 m. = 39.37 in.   1 in. = 0.0254 m.
    1 m. = 1.0936 yd.   1 yd. = 0.9144 m.
    1 rod = 5.029 m.   1 m. = 0.1988 rod
    1 km = 1000 m.   1 m. = 0.001 km.
    1 km = 0.621 mi.   1 mi. = 1.6103 km.

SQUARE MEASURES

    Common Usage   Reciprocal Value
    1 sq. ft. = 144 sq. in.   1 sq. in = 0.0069 sq. in.
    1 sq. yd. = 9 sq. ft.   1 sq. ft. = 0.1111 sq. yd.
    1 sq. rod = 30.25 sq. yd.   1 sq. yd. = 0.0331 sq. rods
    1 sq. mi. = 640 acres   1 acre = 0.0016 sq. mi.
         
METRIC
    1 sq. cm. = 0.1550 sq. in.   1 sq. in. = 6.452 sq. cm.
    1 sq. ft. = 0.0929 sq. m.   1 sq. m. = 10.7643 sq. ft.
    1 sq. m. = 1.196 sq. yd.   1 sq. yd. = 0.8361 sq. m.
    1 hectare = 2.47 acres   1 acre = 0.4049 hectares
    1 sq. km. = 0.386 sq. mi.   1 sq. mi. = 2.59 sq. km.

  AWG to Metric Conversion - American Wire Gauge Conversion Chart
AWG mm2   AWG mm2
30 0.05   8 10
28 0.08   6 16
26 0.14   4 25
24 0.25   2 35
22 0.34   1 50
21 0.38   2/00 70
20 0.5   3/00 95
18 0.75   4/00 120
18 (UL) 1   300MCM 150
17 1   350MCM 185
16 1.5   500MCM 240
14 2.5   600MCM 300
12 4   750MCM 400
10 6   1000MCM 500