Table  of conversion  
 
 
UNIT A   UNIT B S P A C E UNIT C   UNIT D
1 acre = 0.4047 hectares   1 kg = 35.3 ounces
1 sq.acre = 1/ 247 sq. km   1 kg =  2.2046 pounds
1 sq.acre = 4047 sq. m   1 kg =1 / 1000   tons *
1 sq.acre = 1/ 640  sq. miles *   1 kg = 1/ 1016 tons (UK/long)
1 barrel (oil) = 1/ 6.29 cub.metres   1 kg = 1/ 907 tons (US/short)
1 barrel (oil) = 34.97 gallons (UK)   1 km =  1000  meters *
1 barrel (oil) = 42   gallons (US) *   1 km =  0.6214 miles
1 barrel (oil) = 159 litters   1 liter =  61.02 cub.inches
1 cm = 1/ 30.48  feet *   1 liter =  0.2200 gallons (UK)
1 cm = 1/ 2.54  inches *   1 liter =  0.2642 gallons (US)
1 cm = 1/ 100  meters *   1 liter =  1.760 pints (UK)
1 cm = 10  millimeters *   1 liter =  2.113 pints (US liq.)
1 cubic cm = 0.06102 cubic inches   1 m = 1/ 0.9144  yards *
1 cubic cm = 1/ 1000  liters *   1 m = 100  cm *
cubic cm = 1 milliliter *   1 mile = 1.609 km
1 cubic foot = 1728   cubic inches *   1 millimeter = 1/ 25.4  inches *
1 cubic foot = 0.0283 cubic meters   1 ounce = 28.35 grams
1 cubic foot = 1/ 27  cubic yards *   1 pint (UK) = 0.5683 liters
1 cubic foot = 6.229 gallons (UK)   1 pint (UK) =  1.201 pints (US liq.)
1 cubic foot = 7.481 gallons (US)   1 pint (US liq.) =  0.4732 liters
1cubic foot = 28.32 liters   1 pint (US liq.) =  0.8327 pints (UK)
1 cubic inch = 16.39 cubic cm   1 pound =  0.4536 kg
1 cubic inch = 0.01639 liters   1 pound =  16  ounces *
1 cubic meter = 35.31 cubic feet        
        1 sq. cm =  0.1550 sq. inches
1 foot = 30.48  centimeters *   1 sq. feet =  144  sq. inches *
1 foot = 0.3048  meters *   1 sq. feet =  0.0929 sq. m 
1 foot = 1/ 3 # yards *   1 sq. inches =  6.4516  sq. cm *
1 fl.ounce (UK) = 0.961 fl.ounces (US)   1 sq. inches = 1/ 144   sq. feet  *
1 fl.ounce (UK) = 28.41 milliliters   1 sq. km = 247 acres
1 fl.ounce (US) = 1.041 fl.ounces (UK)   1 sq. km =  100   ha *
1 fl.ounces (US) = 29.57 milliliters   1 sq. km =  0.3861 sq. miles
1 gallon = 8  pints *   1 sq. m  = 1/ 4047 acres
1 gallon (UK) = 0.1605 cubic feet   1 sq. m  = 1/ 10 000  ha *
1 gallon (UK) = 1.2009 gallons (US)   1 sq. m  = 10.76 sq. feet
1 gallon (UK) = 4.54609  liters *   1 sq. m  = 1.196 sq. yards
1 gallon (US) = 0.1337 cubic feet   1 sq. mile = 640  acres *
1 gallon (US) = 0.8327 gallons (UK)   1 sq. mile = 259 ha
1 gallon (US) = 3.785 liters   1 sq. mile = 2.590 sq. km
1 gram = 1/ 1000  kilograms  *   1 sq. yard = 1/ 1.196 sq. m 
1 gram = 1/ 28.35 ounces   1 tone  =  1000  kg *
1 hectare =  2.471 acres   1 tone  =  0.9842 tons (UK/long)
1 hectare = 1/ 100  sq. km *   1 tone  = 1.1023 tons (US/short)
1 hectare = 10000  sq. m    1 tone (UK/long) = 1016 kg
1 hectare = 1/ 259 sq. miles   1 tone (UK/long) = 1.016 tons
1 hectare =  11 960 sq. yards   1 tone (US/short) = 907.2 kg
1 inch = 1/ 12  feet *   1 yard = 0.9144  m *
1 inch =  2.54   cm *   1 tone (US/short) = 0.9072 tons
1 lbf  = 4.4482  N   1 kgf  = 9.8065 N
1 N/sq.m = 1  Pa 1 bar   =  100000 Pa
1 lbs./sq.inch = 1 PSI 1 lbs./sq.inch =6.89475  KPa
1 ft lbf   = 1.356 J 1 kW h  = 3600    KJ
1 therm  = 105.51  MJ 1 kcalorie   = 4.1868  KJ
1 BTU  = 1.0551  KJ 1 lbf ft  =1.3558  N m
1 hp  =0.745 9  kW ft.lbf /s  = 1.356  W
1 ft/s  = 0.3048 m/s 1 mi/hr  = 1.6093  km/hr

/  means 'divide by'  - *  means it is an exact value