MEP Unit Converter
How the formula works
A unit converter changes a value from one unit to another without changing the quantity it describes. This converter uses a common base unit for each category. The value is first converted to the base unit and then to the unit you want.
Conversion formula
Result = value x (factor of the From unit / factor of the To unit)
The factor of a unit is the number of base units in one of that unit.
Temperature formulas
deg F = deg C x 1.8 + 32
K = deg C + 273.15
deg R = deg F + 459.67
Temperature uses formulas and not a single factor, because the scales start at different zero points.
Where
- Base units used: metre (length), square metre (area), cubic metre (volume), cubic metre per second (flow), pascal (pressure), watt (power), joule (energy), kilogram (mass), metre per second (velocity), watt per square metre kelvin (U-value), lux (illuminance), kelvin (temperature)
- The factors are exact or rounded to at least 8 significant digits
Key MEP conversion factors
- Pressure: 1 bar = 100 kPa = 14.504 psi = 10.197 m of water. 1 psi = 6.895 kPa. 1 atm = 101.325 kPa. 1 kgf/cm2 = 98.0665 kPa.
- Water head: 1 m of water = 9.80665 kPa = 3.281 ft of water. 1 psi = 2.307 ft of water.
- Flow: 1 L/s = 3.6 m3/h = 15.85 US gpm = 2.119 CFM. 1 CFM = 1.699 m3/h. 1 US gpm = 0.2271 m3/h. 1 KLD = 1 m3/day.
- Power: 1 TR = 12,000 BTU/h = 3.517 kW. 1 kW = 3412 BTU/h = 1.341 HP. 1 HP = 0.7457 kW.
- Energy: 1 kWh = 3.6 MJ = 3412 BTU = 860 kcal. 1 TR-hour = 3.517 kWh.
- Length and area: 1 ft = 0.3048 m. 1 m2 = 10.764 ft2.
- Velocity: 1 m/s = 196.85 FPM = 3.281 ft/s.
- Illuminance: 1 foot-candle = 10.764 lux.
- U-value: 1 BTU/(h.ft2.F) = 5.678 W/(m2.K).
How to use the converter
- Select the category, then the From unit and the To unit.
- Enter the value you want to convert.
- Optionally choose the number of decimal places, or ask to see the value in all other units of the category.
- Click Calculate, then Download PDF Result if you need a record.
Important notes
- Pressure units based on a column of water or mercury use standard values. 1 m of water is taken as 9.80665 kPa (water at about 4 deg C).
- Gallon units are the US gallon (3.785 L), except where “UK gal” (4.546 L) is written.
- HP means mechanical horsepower (745.7 W). PS is the metric horsepower (735.5 W).
- BTU and kcal use the International Table values, the common ones in HVAC work.
Worked example
Example 1 – Pressure: psi to bar
A pump gauge reads 150 psi. 1 psi = 0.068948 bar.
150 x 0.068948 = 10.3421 bar (1034.2 kPa).
Example 2 – Pressure to water head
A pump gives a pressure of 6 bar. 1 bar = 10.197 m of water.
6 x 10.197 = 61.18 m of water. In other units this is 600 kPa, 87.02 psi and 200.7 ft of water.
Example 3 – Cooling capacity: TR to kW
A chiller is rated 1.5 TR. 1 TR = 3.5169 kW.
1.5 x 3.5169 = 5.275 kW (18,000 BTU/h).
In the other direction, 100 kW = 100 x 0.28435 = 28.43 TR.
Example 4 – Airflow: CFM to L/s and m3/h
An air handler moves 1000 CFM. 1 CFM = 0.47195 L/s = 1.699 m3/h.
1000 x 0.47195 = 471.95 L/s, or 1699 m3/h.
For water, 500 US gpm = 500 x 0.22712 = 113.56 m3/h.
Common mistakes
- Mixing the US gallon and the imperial (UK) gallon. They differ by about 20 %, so check which one your data uses.
- Confusing the three kinds of tons. A ton of refrigeration (TR) is 3.517 kW. A metric tonne is 1000 kg. A US short ton is 907 kg.
- Using 1 kg/cm2 as 1 bar. They are close (1 kgf/cm2 = 0.98 bar) but not equal, which matters for precise work.
- Mixing gauge and absolute pressure. Unit conversion does not change this, so keep track of whether your value is gauge or absolute.
- Forgetting that temperature needs a formula, not a factor. A temperature difference of 10 deg C is 18 deg F, but a temperature of 10 deg C is 50 deg F.
- Using HP and kW as if they were the same. A motor in HP is a mechanical output, and its electrical input is higher.
- Reading BTU/h as BTU. BTU/h is a rate of power, and BTU is an amount of energy.
- Using CFM as a volume. CFM is a flow, cubic feet per minute, and ft3 is a volume.
- Rounding too early. Keep extra digits during calculation and round only the final result.
Frequently asked questions
How do I convert psi to bar?
Multiply psi by 0.068948. For example, 150 psi = 10.34 bar. To convert bar to psi, multiply by 14.504.
How do I convert bar to metres of water head?
Multiply bar by 10.197. A pressure of 6 bar equals about 61.2 m of water head.
How many kW is 1 TR?
1 TR = 3.517 kW of cooling = 12,000 BTU/h. The electrical power the chiller uses is different and depends on its efficiency.
How do I convert CFM to m3/h and L/s?
1 CFM = 1.699 m3/h = 0.4719 L/s. For example, 1000 CFM is 1699 m3/h or 471.9 L/s.
How do I convert gpm to m3/h?
Multiply US gpm by 0.2271. For example, 500 gpm = 113.6 m3/h. One US gpm is also 0.06309 L/s.
What is KLD?
KLD means kilolitres per day. 1 KLD = 1 m3/day = 1000 litres per day. It is used for water and sewage plant capacity.
What is MGD?
MGD means million gallons per day, in US gallons here. 1 MGD = 3785.4 m3/day = 3785.4 KLD.
How do I convert kWh to BTU?
1 kWh = 3412.14 BTU. The reverse is 1 BTU = 0.000293 kWh.
What is the difference between HP and kW?
1 mechanical HP = 0.7457 kW. HP is often the mechanical output of a motor, and the electrical input is higher because of losses.
How do I convert Celsius to Fahrenheit?
F = C x 1.8 + 32. For example, 25 deg C is 77 deg F. Remember that a temperature difference is only multiplied by 1.8 and does not add 32.
How accurate are the conversion factors?
Factors are exact or rounded to at least 8 significant digits. This is more than enough for design and site work, but check your contract if you need a specific rounding rule.
Can I convert more than one unit at a time?
Yes. Choose “Show the value in all other units of this category” to see the same value in every unit in one result.