| °C | degree Celsius |
| °F | degree Fahrenheit |
| barg | gage pressure in bar |
| btu/hr | heat transfer unit, British Thermal Unit (BTU) per hour (hr) |
| CA | compressed air |
| cfh | flowrate in cubic feet per hour |
| cm | centimeter |
| cm W.C. | pressure in centimeters of water column |
| D | diameter |
| D, in | diameter in inch |
| DB | dry bulb temperature |
| DP | dew point temperature |
| EG | ethylene glycol |
| ft | unit of length, foot |
| gph | US gallons per hour |
| gpm | US gallons per minute |
| in | inch |
| in Hg | pressure or vacuum in column of mercury in inches |
| in W.C. | pressure in inches of water column |
| IP | Imperial Units |
| kg | kilogram |
| kg/hr | mass flow in kilograms per hour |
| kw | unit of heat transfer in kilowatts, 1 kw = 1000 watts = 3412 btu/hr of heat transfer rate |
| kw | unit of electric power = 1000 watts |
| l | litter |
| lbs/hr | mass flow in pounds per hour |
| lpm | litters per minute |
| lps | litters per second |
| m | meter |
| mm | millimeter |
| NG | natural gas |
| Nm^3 / hr | flowrate in Normal cubic meters per hour |
| P | pressure |
| pa/m | pressure drop in Pascal per meter |
| PD | pressure drop |
| PD, kpa/m | pressure drop in kilopascal per meter |
| PG | propylene glycol mixture |
| psi /100 ft | pressure drop in 100 feet of pipe in pounds per square inch |
| psig | gage pressure in pounds per square inch |
| RH | relative humidity |
| scfm | flowrate in Standard cubic feet per minute (Standard condition is 68 °F, 36 % relative humidity at sea level). |
| SI | Metric Units |
| temp. | temperature |
| ton | cooling load, equivalent to 12,000 btu/hr for refrigeration cooling and 15,000 btu/hr for cooling tower cooling |
| V | velocity |
| V, fpm | velocity in feet per minute |
| V, fps | velocity in feet per second |
| WB | wet bulb temperature |
| ΔT | measure of temperature rise (heating) or temperature drop (cooling) |
