The truth on proper tank sizes and actual gallons vs. nominal gallons.

When ordering a storage tank, manufacturers often give you nominal gallons which normally include the space on the elliptical heads as storage area. Please be aware that many manufacturers often claim that for example a 42″ diameter x 85″ OAL tank holds 504 gallons, when in reality it only holds 460 actual gallons.

The below calculator will give you a true calculation for choosing a proper tank size for your needs.


  1. 1. Enter the OD (Outside Diameter)
  2. 2. Enter the OAL (Overall Length)
  3. 3. Click Submit

Tank Size Calcualtor

OD (Outside Diameter)

OAL (Overall Length)