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.

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

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

Friction Loss Calculators:
Friction loss calculations are for standard PVC pipe.
Cl 160 PVC pipe is not commonly available in 1/2" size, therefore the calculator assumes that Cl 315 pipe will be substituted.
Cl 200 PVC pipe is not commonly available in 1/2" size, therefore the calculator assumes that Cl 315 pipe will be substituted.
Cl 160 PVC pipe is not commonly available in 3/4" size, therefore the calculator assumes that Cl 200 pipe will be substituted.
This calculator uses a contracted form of the Hazen-Williams formula which is the industry standard for calculating friction loss.
A conservative C coefficient of 140 is used for PVC pipe (many authorities use 150 which is risky as it leaves no margin for error).
Velocities over 7 feet per second should not be allowed in PVC pipe.
Velocities over 5 feet per second should be avoided, especially with pressures higher than 80 PSI, or in pipe larger than 2".

Or you can make use of Metric Conversions online to work it out for you