How do I calculate tank volume?

Tank volume depends on the tank shape and inside dimensions. Cylinders use circular area times length or height, rectangles use length times width times height, and curved tanks need shape-specific formulas for partial fill.

Why is partial fill harder for horizontal tanks?

Horizontal tanks fill through a curved cross-section, so the relationship between depth and stored volume is not linear.

Should I use inside or outside dimensions?

Inside dimensions are more accurate because wall thickness and end construction reduce the actual liquid capacity.

Free tank capacity calculator

Tank Volume Calculator

Calculate total tank capacity and current fill volume for vertical, horizontal, rectangular, and elliptical tanks in gallons, liters, and cubic feet.

Liquid storage planning

Tank volume inputs

Full and partial fill

Tank shape

Length unitResult gallons

Tank diameterTank heightCurrent fill depth

Quick examples

Filled volume (US gal)

3,384.11

Filled volume (L)

12,810.2

Total capacity (US gal)

4,512.14

Total capacity (cu ft)

603.19

Fill level

75%

Empty remaining

1,128.04 gal

Related volume tools

Pool Calculator

Plan volume, excavation, liner area, perimeter, and surrounding deck takeoffs for common pool shapes.

Pool Volume Calculator

Calculate pool volume for rectangle, circular, and oval pools with flat or sloped depths.

Cubic Feet Calculator

Calculate cubic feet for boxes, rooms, and cylinders with cubic yard and metric conversions.

Cubic Meter Calculator

Calculate cubic meters for boxes, rooms, and cylinders with liters and imperial conversions.

Pond Calculator

Estimate pond volume, liner size, excavation, edging length, and pump flow for garden and koi ponds.

Gallons to Ounces Converter

Convert US or imperial gallons to fluid ounces, cups, pints, quarts, liters, and milliliters.

What this tank volume calculator measures

This calculator estimates total tank capacity and current filled volume for several common storage shapes: vertical cylindrical tanks, horizontal cylindrical tanks, rectangular tanks, and elliptical tanks. It is useful for water storage, fuel tanks, process tanks, troughs, utility reservoirs, and general liquid storage planning.

Full tank and partial fill volume

The tool does more than calculate full capacity. It also uses the current fill depth to estimate how much liquid is actually in the tank right now. That matters when you are reading a dip stick, float level, sight tube, or manual gauge and need to convert that depth into gallons or liters.

Why shape matters

Rectangular and vertical cylindrical tanks fill in a simple linear way, so doubling the fill depth doubles the stored volume. Horizontal cylinders and elliptical tanks do not behave like that because the shape curves at the sides. A half-full reading by depth does not always mean exactly half the volume, which is why shape-specific math matters for an accurate estimate.

Planning notes

Use inside dimensions when possible, especially if wall thickness is significant. Real installed capacity can also change slightly with end caps, baffles, fittings, and internal hardware. For billing, custody transfer, or regulated storage, use the manufacturer chart or calibrated tank table. For practical field planning, this calculator should give a solid estimate.