Storage tank manufacturers may use either actual or nominal gallon capacities. Nominal gallons normally include the space on the elliptical heads as storage area (white area in image below).
For example, a 42" outside diameter x 84" overall length tank holds approximately 504 nominal gallons, when in reality it only holds approximately 456 actual gallons.
The below calculator will give you a close approximation calculation for choosing a proper tank size for your needs.
ID (Inside Diameter) -
Approx. Actual Gallons -
Approx. Nominal gallons -
Approx. actual gallons includes the area in Blue. Approx. nominal gallons includes the areas in Blue and White combined. Area in Grey is not included in either Approx. nominal or Approx. actual gallon capacity.
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