Conversion between different units of quantities

Energy
1kWh = 3.6x10⁶ J
1 eV = 1.6x10^-19 J

Time
1 year = 3.154x10⁷ s

Pressure
1 Pa = 1 Nm^-2

Density
1 kgm^-3 = 10^-3 gcm^-3

Speed
1 ms^{- 1} = 3.6 kmhr^-1

Conversion between metric units and imperial units

Length
1 metre (m) = 3.281 feet 1 foot (ft) = 0.3048 metres
1 yard = 3 feet = 0.914 m 1 metre = 1.09 yards
1 mile = 1760 yards = 1606 m = 1.6 km
1 km = 0.621 miles ( 1 km is about 5/8 of a mile)

Area
1 square metre = 10.764 square feet = 1.196 square yards
1 square yard = 0.836 square metres
1 square foot = 0.0929 square metres

Mass
1 kilogram (kg) = 2.205 pounds (lb) 1 lb = 0.454 kilograms
1 ounce (oz) = 0.0283 kg = 28.3 grams (gm)

Volume
1 cubic metre = 35.3 cubic feet 1 cubic foot = 0.0283 cubic metres = 6.21 gallons
1 gallon = 0.00456 cubic metres = 4.56 litres = 0.16 cubic feet
1 litre = 0.22 gallons = 0.26 gallons (USA)
1 gallon (USA) = 0.00379 cubic metres = 3.79 litres

Density
1 lb per cubic foot = 0.0016 kg per cubic metre
1 kg per cubic metre = 0.06 lb per cubic foot
The density of water is 1000 kg per cubic metre or 60 lb per cubic foot
1 gallon of water has a mass of 9.67 lb (about 10 lbs)

Force
1 poundal (pdl) = 0.138 N 1 Newton = 7.23 poundals
1 lbf (the weight of a 1 lb mass) = 4.45 N

Pressure
1 lbf per square inch = 6895 Pa 1 Pa = 0.000145 lbf per square inch
The pressure exerted by the Earth's atmosphere at sea level is about 15 lbf per square inch = 15x6895 = 103425 Pa (about 100 000 Pa)
Standard atmospheric pressure is 101 325 Pa = 14.696 lbf per square inch

Energy
1 ft pdl = 0.0421 Joules (J) 1 J = 23.7 ft pdl
1 BTU = 1055 J

Power
1 Horse power (HP) = 746 W 1 W = 0.0013 HP

Speed and velocity
1 metre per second (m/s) = 3.281 feet per second = 2.24 mph
1 mile per hour (mph) = 1.606 km per hour = 0.446 m/s

Useful speed limits:
20 mph = 32 km per hour
30 mph = 48.2 km per hour
60 mph = 96.4 km per hour
70 mph = 112.4 km per hour

20 km per hour = 12.5 mph
30 km per hour = 18.7 mph
40 km per hour = 25.0 mph
50 km per hour = 31.1 mph
90 km per hour = 56.0 mph
110 km per hour = 68.5 mph
120 km per hour = 74.7 mph
130 km per hour = 80.9 mph

Acceleration
1 metre per second squared (m/s²) = 3.28 ft/s²
Standard acceleration of gravity = 32.174 ft/s² = 9.81 m/s²