# Formulas & Conversions

## Conversions

Length:

To get inches when you know millimeters, divide millimeters by 25.4

To get millimeters when you know inches, multiply inches by 25.4

Pressure:

To get bars when you know psi, divide psi by 14.5

To get psi when you know bars, multiply bars by 14.5

Area:

To get square inches when you know square feet, multiply square feet by 144

To get square feet when you know square inches, divide square inches by 144

To get square yards when you know square feet, divide square feet by 9

To get square feet when you know square yards, multiply square yards by 9

Volume:

To get cubic inches when you know gallons, multiply gallons by 231

To get gallons when you know cubic inches, divide cubic inches by 231

To get gallons when you know liters, divide liters by 3.785

To get liters when you know gallons, multiply gallons by 3.785

To get cubic inches when you know liters, multiply liters by 61.0237

To get liters when you know cubic inches, divide cubic inches by 61.0237

To get cubic centimeters when you know cubic inches, multiply cubic inches by 16.387

To get cubic inches when you know cubic centimeters, divide cubic inches by 16.387

To get cubic inches when you know cubic feet, multiply cubic feet by 1728

To get cubic feet when you know cubic inches, divide cubic inches by 1728

Formulas

Circumference of circle:  3.14 x diameter = inches of circumference

Radius of rod or piston:  diameter of rod or piston/2 = length of radius in inches

Rectangular Area:  length in inches x width in inches = square inches

Circular Area:  3.14 x radius of cylinder squared = square inches

Piston area:  3.14 x (piston diameter/2)(piston diameter/2) = square inches

Rod area:  3.14 x (rod diameter/2)(rod diameter/2) = square inches

Cylinder force:  pressure in psi x area of piston exposed to hydraulic oil = pounds force

Cylinder force – extend:  pressure in psi x 3.14 x (piston diameter in inches/2)(piston diameter in inches/2) = pounds force

Cylinder force – retract:  pressure in psi x 3.14 x (piston area – rod area) = pounds force  (see next line)

Cylinder force – retract:  pressure in psi x 3.14 x ((piston diameter in inches/2)(piston diameter in inches/2)-(rod diameter/2)(rod diameter/2)) = pounds force

Cylinder speed: volume of fluid into cylinder in cubic inches per minute/ area of piston = inches per minute.  Divide by 60 to get inches per second

Cylinder speed – extend:  (pump gpm / 231cubic inches in a gallon)/piston area = inches per minute

Cylinder speed – retract:  (pump gpm / 231cubic inches in a gallon)/(piston area – rod area) = inches per minute

Horsepower required to drive a pump:  psi required x gallons per minute required / (efficiency)(1714)  Efficiency is generally 85%, so use 0.85 in the formula.  This formula works for electric motors – a gas or diesel engine will need a higher horsepower rating.

Volume:  length x width x height in inches = cubic inches.  Divide by 231 cubic inches in a gallon to get gallons

Gallons in a cylindrical tank: diameter in inches x 3.14 x length in inches / 231 = gallons in tank

Gallons in a rectangular tank:  length in inches x width in inches x height in inches / 231 = gallons in tank

Weights

Generally accepted values
May vary slightly with material grade and method of processing

Weight of steel:   0.2865 pound per cubic inch, 495 lbs per cubic foot

Weight of aluminum:   0.0955 pound per cubic inch, 165 lbs per cubic foot

Weight of bronze:   0.2947 pound per cubic inch, 509 lbs per cubic foot

Weight of hydraulic oil:   0.0312 pound per cubic inch, 53.9 pounds per cubic foot, 7.2 pounds per gallon

Weight of gasoline:   0.0275 pound per cubic inch, 47.1 pounds per cubic foot, 6.3 pounds per gallon

Weight of diesel fuel:   0.0303 pound per cubic inch, 52.1 pounds per cubic foot, 7.0 pounds per gallon

Weight of water:   0.0361 pound per cubic inch, 62.4 pounds per cubic foot, 8.3 pounds per gallon