# 6.1: Units Related to Water

- Page ID
- 11952

The following unit conversions are directly related to sizing and analyzing rainwater harvesting systems in terms of length, area, volume, mass, pressure, and general water conversions.

## Length

- \(1\; m = 3.28\; ft = 100 \;cm\)
- \(1 \;ft = 12\; in = 30.48\; cm\)
- \(1\; mi = 5,280\; ft = 1.61 \;km\)

## Area

- \(Rectangle: length * width\)
- \(Circle: π * r^2\)
- \(1\; m^2 = 10.765 \;ft^2 \)
- \(1\; km^2 = 0.386\; mi^2 = 1,000,000\; m^2 \)
- \(1\; hectare = 10,000\; m^2 = .01\; km^2 = 2.47\; acres \)
- \(1\; mi^2 = 2.6 \;km^2 = 640 \;acres \)
- \(1\; acre = 4,047 \;m^2 = 43,560 \;ft^2 \;(66\; ft * 660 \;ft) = 1/640\; mi^2 ≈ 40% \;of\; a \;hectare\)

## Volume

- \(Area * depth \)
- \(Rectangular\;Prism: Length * Width * Depth \)
- \(Cylinder: π * r^2 * depth \)
- \(1 \;L = 0.264\; gal = 1000\; cm^3 = 1000 \;ml \)
- \(1 \;m^3 = 1000 \;L = 35.3\; ft^3 = 264 \;gal \)
- \(1\; ft^3 (cf) = 28.32\; L = 7.482\; gal \)
- \(1\; gal = 3.785\; L = 4 \;qt = 16\; cups = 128\; fl. oz. \)
- \(1 \;acre-foot = 43,560\; ft^3 = 325,851 \;gal\)

## Mass

- \(1 \;kg = 1,000 \;g = 2.205\; lb\)
- \(1\; lb = 453.6\; g = 16\;oz\)
- \(1\; US \;short \;ton = 907\; kg = 2,000\; lb\)
- \(1 \;metric\; tonne = 1,000\; kg = 2,205\; lb\)

## Pressure

- \(1MPa = 10\; bar = 9.87 \;atm = 145 \;psi \)
- See water pressure for more

## Water (at 4° C and 1 atm)

- \(Density: 1 \;\frac{g}{ml} = 1 \;\frac{g}{cm^3} = 1\; \frac{kg}{L} = 1,000\; \frac{kg}{m^3} \)
- \(Density: 62.4\; \frac{lb}{ft^3} = 8.34\; \frac{lb}{gal} \)
- \(Pressure: 0.4335 \;psi\; for\; every\; vertical\; foot \;of \;water\)