The second part of unit conversion is the conversion for Length,Mud Weight and Power specially used in the oil field.
The RED number is the conversion unit.
Length
Feet x 0.305 = Meters
Inches x 25.4 = Millimeters
Inches x 2.54 = Centimeters
Centimeters x 0.394 = Inches
Millimeters x 0.03937 = Inches
Meters x 3.281 = Feet
Mud Weight
Pounds/gallon x 7.48 = Pounds/cu ft
Pounds/gallon x 0.12 = Specific gravity
Pounds/gallon x 0.1198 = Grams/cu cm
Grams/cu cm x 8.347 = Pounds/gallon
Pounds/cu ft x 0.134 = Pounds/gallon
Specific gravity x 8.34 = Pounds/gallon
Power
Horsepower x 1.014 = Horsepower (metric)
Horsepower x 0.746 = Kilowatts
Horsepower x 550 = Foot-pounds/sec
Horsepower (metric) x 0.986 = Horsepower
Horsepower (metric) x 542.5 = Foot-pounds/sec
Kilowatts x 1.341 = Horsepower
Foot pounds/sec x 0.00181 = Horsepower
Ref book: 
Formulas and Calculations for Drilling, Production and Workover, Second Edition
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