If you know the approximate diameter you can estimate the volume of a tank in gallons per inch.

*Note: Polyethylene by its nature will
change depending upon temperature. Tanks dimensions will vary from
batch to batch. Poly tank size designations are
nominal. All calculations on this page are approximate.*

D = Inside diameter (inches)

C = Height of cone (inches)

S = Height of sloped floor (inches)

W = Height of vertical walls (inches)

Volume per inch in a tank with vertical walls (gallons) |
D ² X .0034 |

Volume in top cone portion (gallons) |
D ² X .0034 X C / 3 |

Height of sloped floor (3/4" per foot) |
S = D X .75 / 12 |

Volume of sloped portion of tank (gallons) |
D ² X .0034 X S / 2 |

For example, 500 gallon tank, flat floor:

**D = 44" **

**C = 6" **

**W = 71" **

Approximate volumes:

Volume per inch = 44 ² X .0034 = 6.6 gallons per inch

Volume of cone = 44 ² X .0034 X 6 / 3 = 13.2 gallons

**Total volume = 6.6 X 71 = 468.6 + 13.2 = 481.8
gallons **

If the 500 gallon tank were a sloped bottom, you would need to calculate the total volume as if it were a flat bottom tank, and then deduct for the sloped portion:

S = 44 X .75 / 12 = 2.75"

Volume of sloped portion = 44 ² X .0034 X 2.75 / 2 = 9.1 gallons

**Total volume of a sloped floor tank = 481.8 - 9.1
= 472.7 gallons **