Measure of distance 

12 inches = 1 foot 

3 feet = 1 yard 

1760 yards = 1 mile 
5,280 feet 
1 inch = 2.54 cm 

1 metre = 1.09 yards 

1 metre = 39.4 inches 

1 furlong = 220 yards 

1 fathom = 6 feet 

1 sea mile = 6080 feet 
1 knot = 1 sea mile per second 
1 Km = 0.621 miles 
conversion factor about 5 / 8 
Measure of area 

484 sq yds = 1 chain 

10 chains = 1 acre 
4840 sq yds; possibly the area of land an ox
could plough in one day 
1 hectare = 10,000 sq metres 
a metric measurement of area 
1 hectare = 2.47 acres 

640 acres = 1 sq mile 

100 hectares = 1 sq Km 

Measure of volume 

1 litre = 1,000 cc 
cubic centimetres 
1 litre = 100 cl 
centilitres; wine bottles hold 70 cl (about six glasses) 
1 litre water weighs 1 Kg 

1 litre = 0.22 gallons 
1.76 pints; to convert litres to gallons divide by 5
and add ten percent 
1 litre = 1.76 pints 

1 gallon = 277 cubic inches 
1 gallon is defined as the volume of 10 lbs of water 
1 cu ft = 6.24 gallons 

1 dram = 1/8 fl oz 

1 teaspoon 
About 5 ml. Teaspoon's vary in size so always
use a calibrated measuring spoon (eg from the chemist) for
medicines, and cooking. 
1 pint 
the volume of 20 fluid ounces of water; about 568 ml 
2 pints = 1 quart 

8 pints = 1 gallon 

500 ml = 0.88 pint 
500 ml is about ten percent short of one pint 
Measure of weight 
Avoirdupois 
16 oz = 1 lb 
lb is shorthand for pound; oz = ounce 
14 lb = 1 stone 

112 lb = 1 cwt 
the weight of a sack of grain 
20 cwt = 1 ton 
2240 lb 
1,000 grams = 1 Kg 

1,000 Kg = 1 metric tonne 

1 kg = 2.2 lb 

1 lb = 454 grams 

1 tonne = 0.984 ton 
one metric tonne is close to one imperial ton 
1 lb = 7000 grains 
the grain was originally the weight of a barley seed 
1 oz troy = 480 grains 
obsolete 
Constants 

Speed of light in vacuum 
3 X 10E8 metres per second; (10E8 = 100 million) 
Speed of sound in air 
1,100 feet per second or about 750 mph or 340 metres
per second 
Radial distance of lightning 
Divide time between flash and bang in seconds by five
to give distance in miles 
pi 
3.1416 or as a fraction about 22 / 7 
1 radian 
57 degrees approx; (360 deg = 2pi radians) 
Base (e) used in natural logs 
2.7183 
Mean radius of earth 
6,371 Km about 
Distance to the moon 
384,400 Km about (centre to centre); one way delay
about one second 
Distance to the sun 
150 million Km about; 500 seconds at the speed of light 
Geosynchronous orbit 
35,786 Km; two way delay about 0.25 second 
Distance to planet Mars 
70 million Km approx; two way delay about ten
minutes 
1 Atmosphere (Bar) 
760 mm column of mercury or a pressure of about 1 Kg
per sq cm (about 15 psi) 
60 mph = 88 feet per second 

1 knot = 1.7 fps about 

50 knots = 58 mph about 

Acceleration due to gravity 
32.2 feet per second per second or 981 cm per sec per
sec 
Specific gravity 

Water 
1 
Brass 
8.5 about 
Copper 
8 
Glass 
2.5 about 
Gold 
19.3 
Iron (wrought) 
7.9 
Lead 
11.4 
Mercury 
13.6 
Platinum 
21.5 
Silver 
10.5 
Alcohol 
0.8 
Methylated spirit 
0.83 
Petrol 
0.7 
Ice 
0.917 
Work and heat 

1 Watt = 1 Joule per sec 
10E7 ergs per sec 
1 Horse Power (HP) 
550 ft lbs per sec or about 746 watts 
1 Kw 
102 Kg metres per sec 
Coefficient of expansion 

Brass 
1.9 X 10E5 
Copper 
1.67 X 10E5 
Iron 
1.1 X 10E5 about; extremes of temperature can
cause railway
track to buckle or fracture, so track must be designed to allow
for this and be monitored. 
Radio 

Boltzmann's constant (k) 
1.38 X 10E23 Joules per deg K or equivalent radio
noise power (kTB) minus 228.6 dbW per deg K per Hz bandwidth. 
Spare 

Disclaimer: this information is provided as a guide for retired people. All numbers are approximate and no liability is accepted for errors.
