Sourcebook of Alternative Technologies for Freshwater Augmentation in some Asian Countries (UNEPIETC, 1998) 
Part D  Annexes 

This water quantity equivalents and conversion factor lists is for those interested in converting units. The righthand column includes units expressed in two systems  US Customary and International System (metric). Units, which are written in abbreviated form below, are spelled out in parentheses the first time they appear. To convert from the unit in the lefthand column to that in the right, multiply by the number in the righthand column. Most of the quantities listed were rounded to five significant figures. However, for many purposes, the first two or three significant figures are adequate for determining many waterquantity relations, such as general comparisons of water availability with water use or calculations in which the accuracy of the original data itself does not justify more than three significant figures. Quantities shown in italics are exact equivalents  no rounding was necessary. Regarding length of time, each calendar year is assumed (for this list) to consist of 365 days.
US Customary 
US Customary or Metric  
Length  
1 in (inch) 
= 
25.4 mm (millimetres) 
1 ft (foot) 
= 
0.3048 m (metre) 
1 mi (mile, statute) 
= 
5280. ft 
= 
1,609.344 m  
= 
1.609344 km (kilometres)  
Area  
1 ft^{2} (square foot) 
0.09290304 m^{2} (square
metre)  
1 acre 
= 
43,560. ft^{2} 
= 
0.0015625 mi^{2}  
= 
0.40469 ha (hectare)  
1 mi^{2} 
= 
640. acres 
= 
259.00 ha  
= 
2.5900 km^{2} (square
kilometres)  
Volume or Capacity (liquid measure)  
1 qt (quart, US) 
= 
0.94635 l(litre) 
1 gal (gallon, US) 
= 
231. in^{3} (cubic
inches) 
= 
0.13368 ft^{3} (cubic
foot)  
= 
3.78541  
= 
0.0037854 m^{3} (cubic
metre)  
1 Mgal (million gallon) 
= 
0.13368 Mft^{3} (million cubic
feet) 
1 Mgal 
= 
3.0689 acreft (acrefeet) 
= 
3,785.4m^{3}  
1ft^{3} 
= 
1,728. in^{3} 
= 
7.4805 gal  
= 
28.317 1  
= 
0.028317 m^{3}  
1 Mft^{3} 
= 
28,317. M^{3} 
1 acreft (volume of water, 1 ft deep, covering an area of 1
acre) 
= 
43.560.ft^{3} 
= 
0.32585 Mgal  
= 
1,233.5 m^{3}  
1 mi^{3} (cubic mile) 
= 
1,101.1 billion gal 
= 
147.20 billion ft^{3}  
= 
3.3792 million acreft  
= 
4.1682 km^{3} (cubic
kilometres)  
Speed (or, when used in a vector sense,
velocity)  
1 ft/s (foot per second) 
= 
0.3048 m/s (metre per second) 
= 
0.68182 mi/hour (mile per hour)  
1 mi/hr 
= 
1.4667 ft/s 
= 
0.44704 m/s  
Volume per Unit of Time (discharge, water supply, water use,
and so forth)  
1 gpm (gallon per minute) 
= 
0.00144 mgd (million gallons per day) 
= 
0.0022280 ft^{3}/s (cubic foot per
second)  
= 
0.0044192 acreft/d (acrefoot per day)  
= 
3.7854 l/min (litres per minute)  
= 
0.063090 l/s (litres per second)  
1 mgd 
= 
694.44 gal/min 
= 
1.5472 ft^{3}/s  
= 
3.0689 acreft/d  
= 
1,120.0 acreft/d (acrefeet per year)  
= 
0.043813 m^{3}/s (cubic metre per
second)  
= 
3,785.4 m3/d (cubic metres per day)  
1 billion gal/yr (billion gallons per year) 
= 
0.0013817 km^{3}/yr (cubic kilometre per
year) 
1 ft^{3}/s 
= 
2.7397 mgd 
= 
448.83 gal/min  
= 
0.64632 mgd  
= 
1.9835 acreft/d  
= 
723.97 acreft/yr  
= 
28.317 l/s  
= 
0.028317 m^{3}/d  
= 
2,446.6 m^{3}/d  
= 
0.00089300 km^{3}/yr  
1 acreft/yr 
= 
892.74 gal/d (gallons per day) 
= 
0.61996 gal/min  
= 
0.0013813ft^{3}/s  
= 
3.3794 m^{3}/d  
1 acreft/d 
= 
0.50417 ft^{3}/s 
Volume, Discharge or use per Unit of
Area  
1 in of rain or runoff 
= 
17.379 Mgal/mi^{2} 
= 
27,154. gal/acre (gallons per acre)  
= 
25,400.
m^{3}/km^{2} (cubic metres per
square kilometre)  
1 in/yr 
= 
0.047613 (Mgal/d)/mi^{2} 
= 
0.073668 (ft/s)/mi^{2}  
1 (Mgal/d)/mi^{2} 
= 
21.003 in/yr (inchesof rain or runoff  per
year) 
1 (ft^{3}/s)/mi^{2} 
= 
13.574 in/yr 
= 
0.010933
(m^{3}/km^{2} (cubic metre per
second per square kilometre)  
Mass (pure water in dry air)  
1 gal at 15° Celsius (59° Fahrenheit) 
= 
8.3290 lb (pounds avoirdupois) 
1 gal at 4° Celsius (39.2° Fahrenheit) 
= 
8.3359 lb 
1 lb 
= 
0.45359 kg (kilogram) 
1 ton, short (2,000 lb) 
= 
0.90718 Mg (megagram) or ton, metric 
Prepared by John C. Krammer, US Geological Survey (National Water Summary 19901991)