📖 How To Use
How to Use the Tank Refill Time Calculator
Getting an accurate refill estimate takes under a minute:
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Enter the tank volume
Input your tank's total capacity — or use the volume you actually need to fill. Select the matching unit: litres, US/UK gallons, cubic metres or cubic feet. If you don't know the volume, use our
Rectangular Tank Volume Calculator first.
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Enter the flow rate
This is the speed at which water enters the tank — your pump's delivery rate or the rated flow of your pipe. Check your pump's data plate (usually stamped in L/min or GPM). Select the matching unit from the dropdown.
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Set the fill percentage (optional)
If you're not starting from empty, adjust this to reflect how much of the tank actually needs filling. For example, if the tank is already 40% full, set this to 60%.
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Hit Calculate
Refill time appears instantly in seconds, minutes, hours, and days. Copy or print the results with one click.
Important: Always use the net delivery rate — the actual flow reaching the tank, not the pump's rated maximum. Pipe friction, elevation, and fittings reduce real-world flow by 10–40%. If in doubt, run a bucket test: measure how many litres flow in 60 seconds and use that figure.
📐 The Formula
Tank Refill Time Formula Explained
The calculation is straightforward — divide the volume of water needed by the rate at which water arrives:
Refill Time = Volume ÷ Flow Rate
Time (minutes) = Volume (litres) ÷ Flow Rate (litres per minute)
Time (hours) = Volume (litres) ÷ Flow Rate (litres per hour)
Time (seconds) = Volume (litres) ÷ Flow Rate (litres per second)
This calculator converts all inputs to litres and litres-per-minute internally, then derives every other unit from the result. Mixed-unit combinations — such as a tank measured in US gallons and a pump rated in m³/hr — always produce correct output.
Flow Rate Conversion Reference
| Unit | Equals (L/min) | Typical Use |
|---|
| 1 L/min | 1 L/min | Small domestic pumps, water features |
| 1 L/hr | 0.0167 L/min | Drip irrigation, RO filters |
| 1 m³/hr | 16.667 L/min | Commercial pumps, industrial supply |
| 1 US GPM | 3.7854 L/min | US pump ratings, fire hoses |
| 1 US GPH | 0.0631 L/min | Slow-fill agricultural systems |
| 1 UK GPM | 4.5461 L/min | UK/Commonwealth pump ratings |
Common Pump Flow Rates vs. Refill Time (1,000 L tank, full fill)
| Pump Rating | Flow (L/min) | Refill Time | Typical Application |
|---|
| 10 L/min | 10 | ~100 min (1h 40m) | Small domestic booster pump |
| 20 L/min | 20 | ~50 min | Mid-range home pump |
| 40 L/min | 40 | ~25 min | Large residential/small commercial |
| 5 US GPM | 18.9 | ~53 min | Standard US utility pump |
| 1 m³/hr | 16.7 | ~60 min | European commercial pump |
| 100 L/min | 100 | ~10 min | High-capacity fire tank pump |
💡 When to Use This
Common Use Cases for the Tank Refill Time Calculator
🏠
Household Rooftop Tanks
Know exactly when your overhead tank will be full so you can schedule your pump timer — avoiding midnight overflow or morning dry-outs.
🌾
Agricultural Irrigation
Calculate how long to run a borehole pump to fill a field storage tank before the next irrigation cycle.
🏗️
Construction Sites
Estimate how long to run a water bowser pump to fill a concrete-mixing tank or dust-suppression reservoir.
🚒
Fire Fighting Reserves
Verify that a fire-reserve tank can be refilled to minimum capacity within a required time window using your supply pump.
🏊
Swimming Pools
Work out how many hours a garden hose or fill pump needs to run to top up your pool after evaporation or backwash.
🆘
Emergency Preparedness
Plan how quickly you can refill emergency water stores during a mains outage, using a tanker delivery or secondary source.
Pump Sizing Tip: If the calculated refill time is too long for your needs, use this formula in reverse — divide your required volume by your maximum acceptable fill time to find the minimum flow rate your pump must deliver. Then cross-reference with our Pump Horsepower & Flow Rate Calculator.
❓ FAQ
Frequently Asked Questions
How long does it take to fill a 1,000-litre water tank?
It depends entirely on your pump's flow rate. At 20 L/min it takes 50 minutes; at 10 L/min it takes 100 minutes; at 40 L/min it takes just 25 minutes. Use this calculator with your pump's rated flow to get the precise answer for your setup.
What flow rate should I use — the pump's rated maximum or something lower?
Use the actual delivery rate at your operating conditions, not the pump's maximum nameplate rating. Pump output drops with head pressure (the height the water must be pushed) and pipe friction losses. The most accurate approach is a bucket test: time how long it takes to fill a known volume and calculate from there. Real-world delivery is often 20–40% below the rated figure.
How do I calculate tank refill time manually?
Divide the volume to be filled by the flow rate, both in matching units. For example: 500 litres ÷ 25 L/min = 20 minutes. If your units don't match, convert first — 1 US GPM = 3.785 L/min, 1 m³/hr = 16.667 L/min. This calculator handles all conversions automatically.
What is a typical household pump flow rate?
Most domestic booster and pressure pumps deliver between 10 and 50 L/min (2.6 to 13 US GPM) under working conditions. Smaller single-phase pumps typically deliver 15–25 L/min; larger three-phase units can reach 80–200 L/min. Always check the pump's performance curve at your required head pressure, not the headline maximum.
Does pipe diameter affect refill time?
Yes — pipe diameter directly affects how fast water can flow under a given pressure. Doubling the pipe diameter can increase flow by four times (flow scales with the square of the radius). However, the pump itself is usually the binding constraint. A large pipe from a small pump won't significantly improve flow; both the supply line and the pump must be appropriately sized for your required fill rate.
How long does it take to fill a 500-gallon tank with a garden hose?
A typical garden hose delivers 9–17 US GPM (34–64 L/min) at full mains pressure. At 10 GPM, a 500-gallon (US) tank takes about 50 minutes. At 5 GPM (more realistic with pressure drop over length), it takes around 100 minutes. Use the fill percentage field if the tank is already partially full.
Can I use this calculator for pools, septic tanks, or industrial vessels?
Yes — the formula applies to any container filled at a known flow rate, regardless of the liquid or the container type. Enter the total volume (use the appropriate volume calculator for irregular shapes) and your supply flow rate, then read the refill time. The only assumption is a constant flow rate throughout the fill; if flow rate changes with pressure (as in variable-speed pumps), use the average rate.
How do I find my pump's flow rate in L/min if it's rated in m³/hr?
Multiply the m³/hr figure by 16.667. So a 3 m³/hr pump delivers 3 × 16.667 = 50 L/min. Alternatively, select "m³/hr" from the flow rate unit dropdown in this calculator and enter the value directly — no manual conversion needed.