# Tank Volume Calculator

Calculate the volume of cylindrical and rectangular tanks in gallons, liters, and cubic feet. Includes fill time estimate at your flow rate for water.

## What this calculates

Whether you are sizing a water storage tank, estimating rainwater collection capacity, or planning a fish pond, knowing exact tank volume is essential. This calculator handles both cylindrical (round) and rectangular (box) tanks and provides volume in gallons, liters, and cubic feet with a fill time estimate.

## Inputs

- **Tank Shape** — options: Cylindrical (Round), Rectangular (Box) — Select the shape of your tank
- **Length / Height** (ft) — min 0 — Height for cylindrical tanks, length for rectangular tanks
- **Width / Diameter** (ft) — min 0 — Diameter for cylindrical tanks, width for rectangular tanks
- **Depth (Rectangular Only)** (ft) — min 0 — Depth/height for rectangular tanks only
- **Fill Flow Rate** (GPM) — min 0 — Water flow rate in gallons per minute for fill time estimate

## Outputs

- **Volume** (gallons) — Total tank capacity in US gallons
- **Volume** (liters) — Total tank capacity in liters
- **Volume** (ft³) — Total tank volume
- **Fill Time** — formatted as text — Estimated time to fill at the specified flow rate

## Details

For cylindrical tanks, the volume formula is V = π x (diameter/2)² x height. For rectangular tanks, it's simply V = length x width x depth. Results are converted to gallons using the factor of 7.48 gallons per cubic foot.

The fill time estimate helps you plan water delivery or pump sizing. A standard garden hose delivers about 5-10 GPM, while a 1-inch well pump typically delivers 10-15 GPM. Municipal water connections usually provide 15-25 GPM depending on line pressure and pipe size.

For real-world applications, keep in mind that tanks are rarely filled to 100% capacity. Most tank manufacturers recommend leaving 5-10% headspace. Underground tanks also have inlet and outlet fittings that reduce usable volume. For septic tanks and cisterns, consult local building codes for minimum capacity requirements.

## Frequently Asked Questions

**Q: How do I calculate a horizontal cylindrical tank?**

A: For a horizontal cylinder, the diameter is the vertical cross-section and the length is horizontal. Enter the length as the height/length field and the diameter as the width/diameter field. The volume formula is the same regardless of orientation.

**Q: What size tank do I need for rainwater collection?**

A: A rule of thumb: 1 inch of rain on 1,000 sq ft of roof yields about 600 gallons. For an average home (2,000 sq ft roof) in an area with 40 inches of annual rainfall, you could collect about 48,000 gallons per year. A 1,000-2,500 gallon tank covers most residential needs.

**Q: How much does a full water tank weigh?**

A: Water weighs 8.34 pounds per gallon. A 500-gallon tank weighs about 4,170 lbs when full, plus the tank itself. A 1,000-gallon tank weighs over 8,340 lbs. Always verify that your foundation or support structure can handle the full weight.

**Q: What flow rate should I use for the fill time?**

A: Common flow rates: garden hose = 5-10 GPM, 1/2-inch supply line at 40 PSI = 6 GPM, 3/4-inch line = 12 GPM, 1-inch well pump = 10-15 GPM, fire hydrant = 500-1,500 GPM. Use the rate that matches your fill source.

**Q: How do I account for oddly-shaped tanks?**

A: For oval or capsule-shaped tanks, calculate the cylindrical body and add the end caps separately. For tanks with tapered sides, calculate as a frustum or use the average of top and bottom dimensions. When in doubt, the manufacturer's spec sheet will list the exact capacity.

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Source: https://vastcalc.com/calculators/construction/tank-volume
Category: Construction
Last updated: 2026-04-21