Useful Conversions
Who needs to know anything about pumps? You do!

Mechanical pumps are the second most common machine in the world, after electric motors.

Metric to U.S. System Conversions, Calculations, Equations and Formulas:

  • Millimeters (mm) x 0.03937 = inches (")(in)
  • Centimeters (cm) x 0.3937 = inches (")(in)
  • Meters (m) x 39.37 = inches (")(in)
  • Meters (m) x 3.281 = feet (')(ft)
  • Meters (m) x 1.094 = yards (yds)
  • Kilometers (km) x 0.62137 = miles (mi)
  • Kilometers (km) x 3280.87 = feet (')(ft)
  • Liters (l) x 0.2642 = gallons (U.S.)(gals)
  • Liters (l) x 0.0353 = cubic feet
  • Bars x 14.5038 = pounds per square inch (PSI)
  • Kilograms (kg) x 2.205 = Pounds (P)
  • Kilometers (km) x 1093.62 = yards (yds)
  • Square centimeters x 0.155 = square inches
  • Square meters x 10.76 = square feet
  • Square kilometers x 0.386 = square miles
  • Cubic centimeters x 0.06102 = cubic inches
  • Cubic meters x 35.315 = cubic feet


U.S. to Metric Conversions, Formulas, Calculations and Equations:

  • Inches (")(in) x 25.4 = millimeters (mm)
  • Inches (")(in) x 2.54 = centimeters (cm)
  • Inches (")(in) x 0.0254 = meters (m)
  • Feet (')(ft) x 0.3048 = meters (m)
  • Yards (yds) x 0.9144 = meters (m)
  • Miles (mi) x 1.6093 = kilometers (km)
  • Feet (')(ft) x 0.0003048 = kilometers (km)
  • Gallons (gals) x 3.78 = liters (l)
  • Cubic feet x 28.316 = liters (l)
  • Pounds (P) x 0.4536 = kilograms (kg)
  • Square inches x 6.452 = square centimeters
  • Square feet x 0.0929 = square meters
  • Square miles x 2.59 = square kilometers
  • Acres x 4046.85 = square meters
  • Cubic inches x 16.39 = cubic centimeters
  • Cubic feet x 0.0283 = cubic meters

Area and Distance Conversions, Equations, Calculations and Formulas:

  • Acre x 43560 = square feet
  • Inches x 0.0833 = feet
  • Feet x 12 = inches
  • Square mile ("Sections") x 640 = Acres
  • Miles x 5280 = feet
  • Circumference of circle x 0.3183 = Diameter of the circle
  • Diameter of circle x 3.14 = Circumference of circle
  • Diameter squared x 0.7854 = Area of circle
  • Radius squared x 3.14 = Area of circle
  • Miles x 1760 = yards
  • Square Miles x 259 = hectares
  • Square kilometers x 100 = hectares
  • Acres x 40.47 = areas
  • Hectares x 100 = areas
  • Areas x 100 = square meters
  • Yards x 3 = feet
  • Acres x 4840 = square yards

Water Pressure Equations, Conversions, Formulas and Calculations:

  • Feet head (of water) x .433 = Pounds per square inch (PSI)
  • Feet head (of water) x 0.3049 = meters head (of water)
  • Feet head (of water) x 0.0295 = atmospheres
  • Feet head (of water) x 2.988 = kiloPascals
  • Meters head (of water) x 3.28 = feet head (of water)
  • atmosphere (Atm) x 1.013 = 1 bar (b)
  • atmosphere x 14.696 = Pounds per square inch (PSI)
  • bars x 1.033 = kilograms per square centimeter
  • bars x 14.67 = Pounds per square inch (PSI)
  • bars x 100 = kiloPascals
  • Kilograms per square centimeter x 14.223 = pounds per square inch (PSI)
  • Pounds per square inch (PSI) x 2.31 = feet head (ft. hd.)
  • Pounds per square inch (PSI) x 0.0703 = kilograms per square centimeter
  • Pounds per square inch (PSI) x 0.06895 = bars
  • Pounds per square inch (PSI) x 0.06805 = atmospheres
  • Pounds per square inch (PSI) x 2.31 = feet head (of water)
  • Pounds per square inch (PSI) x 6.896 = kiloPascals
  • kiloPascal x 0.145 = Pounds per square inch (PSI)
  • kiloPascal x 0.01 = bars
  • kiloPascal x 0.334 = feet head (of water)

Flow and Water Volume Formulas, Conversions, Calculations and Equations:

  • U.S. Gallons per minute (gpm) x .1337 = Cubic feet per minute
  • Cubic feet per minute x 7.48 = U.S. gallons per minute
  • Cubic feet per second x 448.8 = U.S. gallons per minute
  • U.S. gallons per minute x 0.00223 = Cubic feet per second
  • Acre inches per hour x 453 = U.S. gallons per minute
  • British Imperial gallons x 1.201 = U.S. gallons
  • U.S. gallons x 0.833 = British Imperial gallons
  • Acre feet x 325,850 = U.S. gallons
  • Acre inches x 27154 = U.S. gallons
  • Velocity in feet per second = (0.408 x GPM) / Inside diameter of pipe in inches, squared
  • Q=AV (quantity = area x velocity) ("the basic equation of water flow")
    (example: quantity in cubic feet per second = square feet of area x feet per second velocity)
  • One inch of water depth = 0.62 gallons per square foot of area
  • GPM x 226.8 = liters per hour
  • cubic feet per minute x 1699 = liters per hour
  • acre inches per hour x 1712.3 = liters per minute
  • acre feet x 1231.7 = cubic meters
  • acre inch x 102.64 = cubic meters
  • velocity (feet/second) x 0.3047 = velocity (meters/second)
  • velocity (meters/second) x 3.281 = velocity (feet/second)

Pump Calculations, Conversions, Equations and Formulas:

The following formulas assume 55% pump efficiency (the standard assumption).

Note: Horsepower is Brake horse power for an electric motor. Do not use for fuel-powered pump engines!

  • GPM = (horsepower x 2178) / feet head
  • Feet head = (2178 x horsepower) / GPM
  • Efficiency of pump = (GPM x feet head) / (horsepower x 3960)
  • Horse powers x 745.7 = watts (W)
  • Water flow (in cubic meters per second) = 0.55 x pump power (watts) / pressure (pascals)
  • Water flow (in liters per second) = 5.43 x pump power (kilowatts) / pressure (bars)

Miscellaneous Irrigation Formulas, Conversions, Equations and Calculations:

Sprinkler Precipitation Rate:
Note: "head spacing" is the distance between sprinkler heads. L = length between heads in the row, W = width between rows. Therefore "head spacing " = L x W. Use the GPM value for a full circle sprinkler. So if your sprinklers are all half circles, you need to double the GPM value so it is equivalent to a full circle value.

  1. Precipitation rate for square sprinkler spacing:
    GPM of full circle sprinkler x 96.3) / head spacing in feet = precipitation rate in inches per hour
  2. Precipitation rate for triangular sprinkler spacing:
    (GPM of full circle sprinkler x 96.3) / (head spacing in feet x 0.866) = precipitation rate in inches per hour

Example: Rotors arranged in rows. The rows are 25 feet apart and the sprinklers are 30 feet apart in the row. The heads are arranged in a triangle pattern. The heads use 6 GPM.

(6 x 96.3) / [(25 x 30) x 0.866]

577.8 / [750] x 0.866

577.8 / 649.5

0.89 inches per hour

 
 
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