Part of the Agriculture collection — 4 tools available
Water Tank Calculator — Volume & Fill Time
Calculate water tank volume in gallons and estimated fill time. Works for rectangular, cylindrical, and round tanks based on dimensions and flow rate.
About This Calculator
Whether you're setting up rainwater harvesting for irrigation, planning livestock watering systems, or sizing emergency water storage for your property, knowing your tank's capacity and how long it takes to fill is essential for planning. Cylindrical tanks are the most common type for agricultural and residential use, but calculating their volume requires the cylinder formula that most people haven't used since math class. Flow rate from your pump or well determines fill time, which affects scheduling and system design. Our water tank calculator computes volume in gallons and estimated fill time.
The Formula Behind This Calculator
Volume (cu ft) = pi * (D/2)² * Height Gallons = Cu ft * 7.48 Weight (lbs) = Gallons * 8.34
Understanding the math helps you verify results and make better decisions for your project.
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How to Use
- 1Enter the tank diameter in feet.
- 2Enter the tank height (or length for horizontal cylinders) in feet.
- 3Set the fill level percentage (100% for full capacity).
- 4Enter the fill flow rate in gallons per minute from your pump or hose.
- 5Click Calculate for total gallons and fill time.
When to Use
- →Sizing a water storage tank for rainwater harvesting, livestock watering, or emergency supply
- →Estimating how long it takes to fill a new tank from your well pump or garden hose
- →Determining whether your current tank capacity meets your daily or weekly water demand
Tips
- ✓Measure your actual flow rate by timing how long it takes to fill a 5-gallon bucket — don't rely on pump specs
- ✓Plan for 2-3 days of water reserve when sizing livestock tanks in case of pump failure or power outages
- ✓Install an overflow pipe near the top of the tank to prevent flooding during unattended filling
FAQ
How many gallons per cubic foot of water?
One cubic foot of water equals 7.48 gallons. A standard 8-foot diameter round tank that's 6 feet tall holds approximately 2,257 gallons.
What size water tank do I need for livestock?
Cattle need 15-25 gallons per head per day. A herd of 20 cattle needs 300-500 gallons daily. Size your tank for at least 2-3 days of supply.
How do I calculate flow rate from my hose?
Time how long it takes to fill a 5-gallon bucket. Divide 5 by the time in minutes. A bucket filled in 30 seconds = 10 GPM.
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