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Area

The square metre (m²) is the SI unit of area, the hectare is used for large areas.   The imperial system uses the square yard (yd²) and the acre for large areas.

unit square km. hectare square metre square cm.square mile acre square yard square foot square inch
square kilometre 1 100 1 x 106  0.386 247.105 1196000    
hectare 0.01 1 10000   0.004 2.471 11960 107600  
square metre   0.0001 1 10000     1.196 10.764 1549.44
square centimetre       1         0.155
square millimetre                 0.00155
square mile 2.59 259 2590000   1 640 3097600    
acre   0.4047 4046.86   0.002 1 4840 43560  
square yard     0.8361 8362     1 9 1296
square foot     0.0929 929.1     0.111 1 144
square inch       6.4516       0.00694 1

Calorific Values

The joule per cubic metre (J/m³) is the SI unit of heat content (Calorific Value).   Many Gas or Fuel Engineers prefer the calorific value to be expressed in terms of heat units. the metric system uses the kilocalorie per cubic metre (kcal/m³) and the imperial system the British thermal unit per cubic foot (Btu/ft³)

unit Kilojoule cu. metre Megajoule cu. metre Kilocal. Cu. metre Btu. cu. foot
Kilojoules / cubic metre 1 0.001 0.238846 0.02684
Megajoules / cubic metre 1000 1 238.8459 26.8392
Kilocalarie / cubic metre 4.1868 0.004187 1 0.11237
Btu. /cubic foot 37.258 0.037247 8.89915 1

Energy

The joule is the SI unit of energy. the joule is really a unit of work, being the work done when a force of 1 newton moves through a distance of 1 metre.   Many fuel and gas engineers prefer to use heat units for energy measurement.   The metric unit for heat energy being the calorie (cal) or kilocalorie (kcal) and the imperial unit being the British thermal unit (Btu).

unit joule kilojoule megajoule calorie Kilocalorie B.t.u Therm kilowatt horse power
joule (watt-sec) 1 0.001   0.2388          
kilojoule 1000 1 0.001 238.8 0.2388 0.9479     0.000372
megajoule 1000000 1000 1 238800 238.8 947.9 0.00948 0.2778 0.3724
calorie 4.1868     1 1 x 10-3        
kilocalorie 4186.8 4.187 0.004187 1000 1 3.969   0.001163 0.00156
B.t.u. 1055.06 1.055 0.001055 252 0.252 1   0.000293 0.000393
Therm   105500 105.5   2.52 x 104 100000 1 29.31 39.29
kilowatt hour 3600000 3600 3.6 859800 859.8 3412 0.0341 1 1.341
horsepower hour 2684520 2685 2.685 641300 641.3 2545 0.02545 0.7458 1

Force

The Newton is the SI unit of force, and is defined as the force required on a mass of 1Kg to acheive an acceleration of 1m/sec.sec. (kg.m/s²)   In the metric (MKS) system, the Kg.force (kg.f) is used.   In the imperial system the basic unit of force is the poundal (lb.ft/s²) and the pound-force (lb.f) is also used.

unit   Newton Dyne gram force kilogram force pound force ounce force Poundal
Newton   1 100000   0.102 0.22481 3.5969 7.233
Dyne   0.00001 1 0.0010198 1.02 x 10-6 0.22481 x 10-5   7.231 x 10-5
sthene   1000     102 224.809    
gram force   980.59 1        
Kilogram force   9.8066 9.807 x 105   1 2.20462   70.9316
Pound force   4.4482 444800   0.4535 1   32.174
ounce force   0.278         1 2.0109
Poundal   0.1383 13825.5   0.0141 0.03109   1
ton force   9964.02     1016.048 2240   72069.9

Length

The metre is the SI unit of length. In the metric system the kilometre is used for long distances.   In the imperial system the basic unit is the yard (yd) and for longer distances the mile.   Both metric and imperials systems use other units which are multiples or fractions of the two basic units.

unit kilometre metre centimetre millimetre mile yard foot inch
Kilometre 1 1000     0.621371 1093.613 3280.84  
metre 0.001 1 100 1000   1.09361 3.281 39.37
centimetre   0.01 1 10   0.010936 0.032808 0.3937
millimetre   0.001 0.1 1     0.00328 0.03937
mile 1.609344 1609.344     1 1760 5280  
yard   0.9144 91.44 914.4   1 3 36
foot   0.3048 30.48 304.8   0.333 1 12
inch   0.0254001 2.54001 25.4001     0.0833 1
Furlong   201.168     0.125 220 660  
chain   20.1168     0.0125 22 66  
fathom   1.8288 182.88     2 6 72
nautical mile (UK) 1.85318 1853.18     1.151515 2026.67 6080  
nautical mile (Int) 1.852 1852     1.15078 2025.373 6076.12  

Mass

The Kilogram (kg) is the basic SI unit of mass. In the metric system the tonne (1000Kg) is used for large weights.   The basic unit of mass in the imperial system is the pound (lb), wich is itself sub-divided into ounces for smaller weights and multiiplied by various factors for larger weight units such as the stone , hundredweight and ton.   It should be noted that in the U.S.A. the ton and hundredweight are not the same as in the U.K. and are refered to as the short ton (2000lb) and short hundredweight (100lb).


unit milligram gram Kilogram Tonne Grain Ounce Pound Cwt. Ton
milligram 1 0.001              
gram   1 0.001   15.4324 0.0353 0.002205    
Kilogram   1000 1 0.001  : 35.274 2.20462 0.0197  
Tonne   1000000 1000 1   35270 2205 19.69 0.98421
grain 64.799 0.0648              
ounce (Av)   28.3495 0.02835   437.5 1 0.0625    
Pound (Av)   453.6 0.04536   7000 16 1 0.0089  
Hundredweight   50800 50.8023 0.0508   1792 112 1 0.05
Ton   1016000 1016.05 1.01605   35840 2240 20 1

Power

Power is the rate of work or energy useage. It is usually expressed in energy or work units per unit of time.
The watt (w) is the SI unit of power,being defined as a joule. per. second. (br/> It is common for electric heaters and gas burners to be sized in kilowatt, although many combustion engineers prefer burners to be rated in Btu. per.hour or Kcal.per hour.
Mechanical engineers use work units such as horsepower (hp) or foot pound-force per second (ft lbf/s).


unit watt (joule . Sec. ) Kilowatt Kg. Force metre / sec. cal. / sec. Kilocal. / min Kilocal. / hour foot pound force / sec.foot lb. force / minHorsepower Btu. Hour
Watt (joule sec) 1 0.001   0.2388   0.8598 0.7376     3.412
Kilowatt 1000 1   238.8   859.84 737.46   1.341 3412
Megawatt                    
Kg.force. metre sec 9.8067   1       7.233      
Horsepower (Metric) 735.5   75       543   0.98632  
calorie / sec 4.187       1   3.6 3.0878   0.00562 14.29
Kilocalorie / min                    
Kilocalorie / hour 1.163     0.2777   1 0.8577   0..00156 3.9682
Foot pound force / sec 1.356     0.3239   1.16599 1   0.00182 4.6296
Foot pound force / min                    
Horsepower 745.7 0.7459   178.15   641.36 550 33000 1 2545
B.T.U. / second   1.055                
B. T. U. / hour 0.2931   0.07   0.252 0.216 12.96     1

Pressure

The pascal (Pa) is the SI unit of pressure. The pascal is a very small unit so usually pressures are expressed in Kilopascal (kPa) or megapascal(mPa).
Pressure is force per unit of area, many engineers prefer the more practical units of Pounds force per square inch or Kg force per square meter.
Some engineers prefer to use the very practical units of inches or cm. water or mercury gauge.

unit k-pascal millibar bar Kg. sq. cm. mm. of water cm. of water mm. of Mercury pounds sq.inch inch of water inch of Mercury
"Pascals, N.m3" 0.001 0.01   &bnsp; 0.102          
kilopascals 1 10 0.01 0.010 102     0.145 4.014 0.2953
millibar 0.01 1 0.001   10.2 1.0197     0.4014  
bar 100 1000 1 1.02 10200     14.5 401.4 29.53
Kilograms.force / square cm. 98.07 9807 0.9807 1 10000 1000 735 14.22 393.7 28.96
millimetre of water 0.0098 0.0981   0.0001 1     0.00142 0.0394 0.0029
centimetre of water   0.9807   0.001   1 0.735 0.142 0.394 0.0289
millimetre of Mercury 0.1333 1.3332   0.0013 13.5951 1.36 1 0.0193 0.535 0.0394
Pound Force / sq. in 6.897 68.97 0.069 0.0703 703.2 70.4 51.7 1 27.69 2.037
Inch of water 0.2491 2.4909   0.0025 25.4 2.54 1.87 0.0361 1 0.0736
inch of Mercury 3.386 33.864 0.0339 0.0353 345.3 34.6 25.4 0.491 13.59 1
atmosphere (standard) 101.3 1013.25 1.013 1.033 10330 1033 760 14.696 406.7 29.92

Volume

The cubic metre is the SI unit of volume. The unit of capacity is the litre, being the volume taken up by 1 Kilogram of water at specific temperature conditions, i.e. 1000 cubic centimetres or 1 cubic decimetre.
In the imperial system the gallon is the unit of capacity, being the volume taken up by 10lbs of water at specific temperature conditions

unit cubic metre cubic decimetre (litre) cubic centimetre cubic yard cubic foot cubic inch U.S. gallon Imperial gallon
cubic metre = 1 1000 1 x 106 1.30795 35.3147 61023.7 264.170 219.97
cubic dm (litre) = 0.001 1 1000   0.035315 61.024 0.264 0.220
cubic centimetre =   0.001 1     0.061    
cubic yard = 0.7673 767.3   1 27 46656 202.635 168.75
cubic foot = 0.02832 28.317 28317 0.03704 1 1728 7.505 6.229
cubic inch = 0.000016 0.0163 16.387   0.00057 1.000 0.004 0.004
imperial gallon =   4.5461 4546   0.1604 277.274 1.201 1.000
imperial quart   1.13652            
imperial pint   0.56826 568.26   0.020068 34.677 0.150 0.125
gill   0.142065            
fluid ounce (UK)   0.02841 28.413          
U.S. gallon = 3.785 x 10-3 3.78541 3786 4.951 x 10-3 0.13368 231.000 1.000 0.833

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