How to Convert from Imperial to Metric?

MeyerFire University | G401.05

By Franck Orset

RESOURCES

• One-Page Summary [PDF]
• Notes Page [PDF]​

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TRANSCRIPT

How to convert from Imperial Units to Metric? 

Many tools can be found on internet for rapid conversion of units from one system to the other. Google, for example, can quickly convert many common units. 

Some excel files are also available for a quick conversion. 

The MeyerFire site also has a free unit converter under Toolkit, then Unit Converter. 

For the most common units, used for fire protection, the conversions are calculated as follows. The last video covered converting from Metric to Imperial, but what about the opposite?  

Today we’re talking imperial conversion over to metric.

For fire pumps and water supplies:

Flow is expressed in gpm. One gpm is 3.785 liters per minute, or 0.227 cubic meter per hour. It is also equivalent to 0.063 liter per second or kg per second. 

This means that a 500 gpm flow is 1892 l/min (generally rounded up to 1900 l/min in most NFPA standards) or 113.5 m3/h or 31 l/s or kg/s. 

Pressure is expressed in psi. One psi is 0.069 bar or 6.9 kiloPascal or 0.7 m of water column. 

This means that 175 psi is 12 bars, or 1206 kPa or 123 mH2O. 

Power for diesel engine drives is expressed in horsepower. 1 horsepower is 0.746 kW. 

This means that 200 hp engine is 149 kW. 

Volume for the water tanks is generally expressed in gallons. 1 gallon is 3.785 liters or 0.003785 cubic meter. 

This means that a 135,000-gallon tank is 510,975 liters or 511 m3. 

For sprinkler systems:

Temperature in degrees Fahrenheit. To convert Fahrenheit into Celsius, a formula needs to be applied. If T is the temperature in Fahrenheit, the temperature in Celsius is 5/9 of T minus 32 ((T-32) * 5/9) 

For example, 212°F is 100°C and 32°F is 0°C. The scale for Celsius has been defined under the different state of water under normal pressure conditions, with 0 for the freezing point and 100 for the boiling point. 

K-factor in gpm per square root of psi, as the K factor is defined by the formula Q [Equation]. A K factor of 1 in the Imperial system, corresponds to a K factor of 14.29 in the metric system. 

For example, K5.6 is K80 and K25 is K360. 

Thread and pipe diameters in inches. 1 inch is 2.54 centimeters or 25.4 millimeters. 

For example, a ½ in thread is 13 mm and a 4 in. pipe is a 100 mm pipe. 

Design density in gpm per square foot. One gpm/sq ft is 40.7 liters per minute per square meter or millimeter per minute. 

This means that 0.15 gpm/sq ft is 6.1 l/min/m2 or mm/min. 

Spacing and distances, generally in feet, sometimes in yards. One foot is 0.3048 meter and one yard is 0.91 m. This means, for example, that 20 ft is 6.1 m. 

Area of application in square foot. One square foot is 0.093 square meter. 

This means that 100 sq feet is 9.3 m2 or 2,000 sq ft is 186 m2. 

Speed for the velocity of water inside the pipes, in feet per second. One foot per second is 0.3048 meter per second. 

This means that 20 ft/s is 6.1 m/s. 

For gas protection systems:

Volume, for the application of the system or room size, expressed in cubic foot. One cubic foot is 0.028 cubic meter. This means that 1,000 cu ft is 28.3 m3. 

Weight, for the quantity of gas, expressed in pounds. One pound is 0.45 kg. This means that 250 lbs is 113.4 kg. 

For energy:

Energy delivered by a fire, generally expressed in BTU, or British Thermal Unit. One BTU is 1.055 kiloJoule or 0.252 kilocalorie. 

This means that a 50,000 BTU fire is equivalent to 52,500 kJ or 12,600 kCal. 

Power delivered by a fire, generally expressed in BTU per hour. 1 BTU per hour is 0.2931 Joule per second or Watt. 10,000 BTU/h is 2930.7 Watts. 

Heat flux, generally expressed in BTU per hour and per square foot. One BTU per hour and per square foot is 3.15 Watt per square meter. 

This means that 300 BTU/h/sq ft is 0.95 kiloWatt per square meter.

I am Franck Orset, this is MeyerFire University.