Length and Area        
 
1 Inch = 25.4 mm
inches to centimeters, multiply by 2.54
1 Foot = 12 Inches or 0.3058 Meters    
feet to meters, multiply by 0.3
1 Yard = 3 Feet or 36 Inches or 0.9144 Meters
yards to meters, multiply by 0.91
1 Mile = 1760 Yards, 5280 Feet, 63360 Inches, .869 Nautical miles or 1.609364 kilometers
miles to kilometers, multiply by 1.61

1 Millimeter =                      0.03937 Inch
1 Centimeter = 10 Millimeters or    0.3937 Inch
centimeters to inches, multiply by 0.39
1 Decimeter  = 10 Centimeters or    3.937 Inces
1 Meter      = 10 Decimeters  or    3.2808 Feet or 39.37 Inches
meters to feet, multiply by 3.28
meters to yards, multiply by 1.09
1 Decameter  = 10 Meters      or   32.81 Feet or 393.7 Inches 
1 Hectometer = 10 Decameters  or  328.08 Feet or 3936.96 Inches
1 Kilometer  = 10 Hectometers or 3280.8 Feet or 0.62136 Mile
kilometers to miles, multiply by 0.62
1 Myriameter = 10 Kilometers  or    6.21 Miles 

Acres to hectares, multiply by 0.4
Hectares to acres, multiply by 2.47 

Nautical 
 
1 Fathom = 6 Feet or 1.829 meters
1 Nautical mile = 6,076.12 feet or 1.15078 miles

Fluid 

1 Teaspoon - tsp
1 Tablespoon - tbsp = 1/2 fluid ounce
1 Cup = 8 ounces
1 Pint = 16 ounces or 2 Cups
1 Quart = 32 ounces or 2 pints
1 US Gallon = 128 ounces or 4 quarts or 3.765 Litre
US gallons to liters, multiply by 3.79
1 Imperial gallon = ?
Imperial gallons to liters, multiply by 4.55 

1 Liter = 62.025 cubic inches or .908 dry quarts
1 Liter = 1.0567 liquid quarts, 0.264 Gallons or xx liquid ounces
liters to US gallons, multiply by 0.26 
liters to Imperial gallons, multiply by 0.22

Weight 
grams to ounces, multiply by 0.035
1 Kilogram = 2.2 lbs.
kilograms to pounds, multiply by 2.21
ounces to grams, multiply by 28.35
1 lb. = 0.4535 kg
pounds to kilograms, multiply by 0.45
US ton to kilograms, multiply by 907
British ton to kilograms, multiply by 1016

Temperature 

Convert Celsius to Fahrenheit, multiply by 1.8 and add 32 
Convert Fahrenheit to Celsius, subtract 32 and muliply by .055
0 Degrees C = 32 Degrees F
212 Degrees F = 100 Degrees C

Power 

1 Horsepower = 0.746 KW or 1.014 PS
1 PS = 0.986 HP or 0.736 KW