Tank Fill Time Calculator

How to calculate filling time

1. Enter the volume of water you still want to add. For a partly filled container, do not enter its full capacity.
2. Choose the matching volume unit and enter the flow actually reaching the container. Pick the flow unit separately.
3. If water is also being used or leaving, open Water used while filling, enable it and enter that rate in the same flow unit.
4. Read the estimated duration and net flow. Check Calculation details if needed, or copy the qualified result.

A clear estimate from the measurements you know

• Two basic measurements: water to add and measured inflow.
• Independent volume and flow units, with US and Imperial gallons clearly distinguished.
• Optional water use is subtracted before calculating the duration.
• Readable days, hours, minutes and seconds, with honest rounding and subsecond results.
• A clear explanation when the net flow is zero or negative, rather than an impossible filling time.

When this calculator is useful

• Estimate how long a hose will take to add a known amount of water to a pool or paddling pool.
• Plan a tank, barrel or trough top-up from a measured delivery rate.
• Check how simultaneous water use changes the estimated filling time of a household tank.

Volume to add, inflow and net flow

The volume to add is the amount still missing from your chosen water level. It is not automatically the container's total capacity. This calculator starts from a known volume and does not infer it from a tank shape or water-depth percentage.

Inflow is water actually reaching the container. A pump's advertised maximum may not match delivery through your hose, pipework and height difference. Measure at the point of delivery under representative conditions.

A bucket test measures flow from a known collected volume and elapsed time. Repeat measurements if the flow varies. The separate Bucket Test Flow Rate Calculator helps with that task; it does not transfer private inputs into this page.

If water leaves during filling, net flow is inflow minus that use. The optional water-use value shares the selected flow unit, so changing the flow unit changes the meaning of both typed rates.

For a positive net flow, time equals volume to add divided by net flow, using matching units. Equal inflow and outflow do not raise the level. A larger outflow prevents filling and can lower the level, but this page does not estimate draining time.

One cubic metre is 1,000 litres. US liquid and Imperial gallons are different units. The calculation keeps their exact conversion factors and rounds only the displayed time, not the entered measurements or net flow.

Worked filling-time examples

A tank needs 1,000 L and receives 20 L/min with no water use: 1,000 ÷ 20 = 50 minutes.

A container needs 5 m³ and receives 50 L/min. Convert 5 m³ to 5,000 L, then divide by 50: 100 minutes, or 1 hour 40 minutes.

Adding 30 US gallons at 20 US gal/min takes 1.5 minutes, or 1 minute 30 seconds. Keep the gallon definition the same on both quantities.

A tank needs 600 L, receives 20 L/min and uses 5 L/min while filling. Net flow is 15 L/min, so the estimate is 40 minutes.

If inflow and use are both 20 L/min, net flow is zero. The container will not fill under those unchanged conditions; zero minutes would be misleading.

What the estimate does and does not mean

The model assumes continuous, unchanged inflow and, if enabled, unchanged water use. Changing supply pressure, other fixtures or a float valve can make the real duration different.

Time is shown to the nearest second once it reaches 1 second. About means the mathematical duration was rounded. A positive duration below 1 second stays explicitly less than 1 second; it is never shown as zero.

Days are blocks of 24 elapsed hours, not calendar dates. There is no start time, predicted finishing clock time, time-zone adjustment or countdown.

Use positive volume and inflow values up to 1,000,000,000 in their selected units, with at most 3 decimal places. Enabled water use may be zero and has the same upper limit. These broad software bounds are not equipment recommendations.

Monitor the water level and stop filling appropriately. This calculator is not an automatic shutoff, pump-sizing tool, pressure model, tank-design certificate or drinking-water safety check.

Your measurements and privacy

This calculator performs its arithmetic in your browser. It does not intentionally upload, save or put the entered measurements into a share link. Copy result includes the measurements and a clean calculator link only when you request it.

The website may still load analytics, consent and other site services. Browser-side calculation is not a claim that the whole site is offline or that every service has been independently audited; see the site's privacy and cookie information.