🛢️ Gallon Calculator
Determine how many gallons your tank or container holds—full or partially filled.
Choose the tank shape, enter its dimensions, and adjust the fill percentage to see the current volume in gallons, liters, and other useful units.
Set less than 100% to calculate partial volume.
Capacity at 100% fill (rectangular tank)
89.7662 gallons
Liters (L)
339.8022
Cubic Feet (ftÂł)
12
Cubic Meters (mÂł)
0.339802
How to Use This Calculator
Select the tank shape
Choose rectangular for boxes, aquariums, or pools, or cylindrical for vertical tanks and silos.
Enter tank dimensions
Provide dimensions using inches, feet, centimeters, or meters. Add the fill percentage to account for partial tanks.
Review gallon and metric volumes
Use the gallon, liter, and cubic-foot outputs for ordering liquids, estimating treatment chemicals, or planning shipments.
Formula
Rectangular: Volume = Length Ă— Width Ă— Height
Cylindrical: Volume = π × (Diameter ÷ 2)² × Height
Gallons = Cubic Feet Ă— 7.48052. Fill level applies a percentage multiplier to the calculated volume.
Use the formula breakdown to confirm the calculation logic or perform the conversion manually if needed.
Full Description
Whether you manage aquariums, rainwater harvesting systems, brewery tanks, or fire suppression reservoirs, knowing the exact volume is critical. This calculator covers the most common tank geometries—rectangular and cylindrical—and converts them into US gallons, liters, cubic feet, and cubic meters.
The fill percentage slider helps you track partial capacities, which is useful for dosing chemicals, scheduling tanker deliveries, or estimating how much liquid remains after a withdrawal.
Combine this tool with the Gallons to Pounds Converter or kg to Gallons Converter when you need to translate between volume and weight for logistics or compliance reporting.
Frequently Asked Questions
Does this calculator use US gallons?
Yes, it uses US liquid gallons. For imperial gallons, multiply the result by 0.832674.
Can I calculate horizontal cylindrical tanks?
Horizontal cylinders require a different formula for partial fills. This tool focuses on vertical cylinders; consider a specialised horizontal tank calculator for that geometry.
How precise are the conversions?
The calculator uses exact conversion factors (1 ftÂł = 7.48052 gal; 1 gal = 3.785411784 L). Results are rounded for display but retain full precision internally.
What if my tank has sloped sides?
Approximate it by dividing the tank into simpler shapes (rectangular or cylindrical) and summing their volumes, or use CAD software for complex geometries.