Units Calculator Tool Guide

What this tool does

This tool converts one unit to another within a unit category. For example, feet (a unit in the unit category of length) can be converted to meters (a different unit within the same unit category).

Included unit categories and corresponding units

Angle – deg (degree); rad (radian)

Area – acre; cm2; ft2; hectare; in2; km2; m2; mile2; mm2; yd2

Calculator – Unitless – This is a “special” units category for the specific purpose of performing calculations with the RED Math on-the-fly feature. When you select this units category, notice that the dropdown units selections disappear. Use this selection to perform Math on-the-fly calculations using this notation: “+” (addition); “-” (subtraction);”*” (multiplication); “/” (division); “^” (exponent); and “( )” parenthesis. Note that blank spaces are ignored by Math on-the-fly. For example: 

  • 4+5 = 9
  • 4-5 = -1
  • 4*5 = 20
  • 4 * 5 = 20
  • 4 / 5 = 0.8
  • 4^2 = 16
  • 4^3 = 64
  • ((400*2)+(600*2))/4 = 500.

Density – g/L (grams per liter); g/m3 (grams per cubic meter); kg/L; kg/m3; lb/ft3 (pounds per cubic foot); lb/yd3 (pounds per cubic yard); oz/ft3 (ounces per cubic foot); oz/yd3

Energy – Btu (British thermal units); Cal (calories); GJ (gigajoules); J (joules); kCal (kilocalories); kJ (kilojoules); kWh (kiloWatt hours); MBtu (thousand Btu); MJ (megajoules); MMBtu (million Btu); MWh (megawatt hours); therm

Flow – CFM (cubic feet per minute); gpm (gallons per minute); L/s (liters per second); m3/hr (cubic meters per hour); m3/min (cubic meters per minute); m3/s (cubic meters per second)

Force – lb (pounds); N (newtons); oz (ounces); pdl (poundals)

Length – chain; cm; ft; furlong; hand; in; km; light yr; link; m; mile; mm; naut mile (nautical miles); parsec; rod; yd

Mass – carat; g (grams); grain; kg (kilograms); lb (pounds); mg (milligrams); slug 

Power – GW (gigawatt); hp (horse power); kW (kilowatt); mW (thousand watts); MW (megawatt); W (watt)

Pressure – atm (atmospheres); bar; hPa (hectopascals); inHg (inches of mercury); iwc (inches of water column); kPa (kilopascals); mbar (millibars); mmHg (millimeters mercury); mmwc (millimeters water column); Pa (pascals); psi (pounds per square inch)

R-valueoF·ft2·h/Btu (degrees Fahrenheit, square feet, hour per British thermal units); K·m2/W (kelin, square meters per watt)

R-value per thicknessoF·ft2·h/(Btu·in) (degrees Fahrenheit, square feet, hour per British thermal unit, inch); K·m2/(W·cm) (kelvin, square meter per watt, centimeter)

Speed – ft/min; ft/s (feet per second); knot; kph (kilometers per hour); m/min (meters per minute); m/s (meters per second); mph (miles per hour)

Temperature Difference – [For example, the temperature difference between inside and outside] oC (degrees Celsius); oF (degrees Fahrenheit)

Temperature Measurement – [A temperature measured with a thermometer] oC (degrees Celsius); oF (degrees Fahrenheit); K (kelvin); R (rankine)

Time – day; hr; min; s; yr

1/Time – [For example, the expression ach has units of 1/hr] 1/day; 1/hr; 1/min; 1/s; 1/yr

UA – Btu/(oF·h) (British thermal units, degree Fahrenheit, hour); W/K (watts per kelvin)

U-value – Btu/(oF·ft2·h) (British thermal units per degree Fahrenheit, square foot, hour); W/(K·m2) (watts per kelvin, square meter) 

For more information regarding Math on-the-fly, please see https://www.redcalc.com/red-calc-pro-manual/#math-on-fly.

Volume – bf (board feet); cm3; cup; ft3, gal (gallons); in3; km3; L (liters); m3; mile3; mL; mm3; oz; pt (pints); qt (quarts); tbsp (tablespoons); tsp (teaspoons); yd3 (cubic yards)


  • Because this Unit Calculator is a RED Calc Pro tool, you may document (print or save as a PDF) a report of your unit conversion or Math on-the-fly calculation.
  • You may copy and past your unit conversion or Math on-the fly calculation to another tool. Merely highlight your result, copy it, and then paste it to another tool input box.