Tank Fill Time Calculator
Enter tank capacity, starting volume, and fill rate to calculate fill duration in days, hours, minutes, and seconds.
Use the Tank Fill Time Calculator
Tank & Flow Inputs
Gallons (US)
GPM = gal/min • GPH = gal/hr • LPM = L/min • LPH = L/hr • CFM = ft³/min
Enter tank capacity and fill rate
Estimated Fill Time
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Net rate:
Visualization illustrates level progression based on steady-state flow, not real-time countdown.
Unit Standards & Calculation Limits
• 1 US Gallon = 3.785411784 L • 1 ft³ = 28.316846592 L • 1 m³ = 1,000 L (NIST SP 811 / HB 44).
• Net Flow Model: Fill duration = (Capacity − Current Volume) ÷ (Fill Rate − Drain Rate).
• Steady Flow Boundary: Actual fill duration can increase as backpressure rises or incoming line pressure drops during continuous operation.
Summary
Enter tank capacity, starting volume, and fill rate to calculate fill duration in days, hours, minutes, and seconds.
How it works
- Enter total tank capacity and select your volume unit (gallons, liters, cubic feet, or cubic meters).
- Optionally enter the current starting volume if the tank is already partially filled.
- Enter the fill flow rate and select your flow unit (GPM, GPH, LPM, LPH, or CFM).
- Optionally enter a simultaneous drain or consumption rate to calculate net filling time.
- View the total duration broken down into days, hours, minutes, and seconds.
Use cases
- Estimate fill time for residential swimming pools, hot tubs, or stock tanks.
- Plan rainwater harvesting cistern and agricultural storage tank refills.
- Account for simultaneous drain or outflow demand while refilling a vessel.
- Evaluate pump transfer sizing against needed tank turnaround periods.
Frequently Asked Questions
Last updated: 2026-09-19 ·
Reviewed by Nham Vu