Worked example
Thirty cubic metres is 30,000 litres. At a steady 20 litres per minute, filling takes 1,500 minutes, or 25 hours. Subtract existing water volume if the pool is partially filled.
Method
Convert volume and flow into matching units before dividing: time = required volume / flow rate. Measure flow by timing how long a known-volume container takes to fill. Repeat the measurement if supply pressure changes.
Check the assumptions
Volume is the amount of water; flow rate is the amount delivered per unit of time. A constant-rate estimate excludes pauses, leaks, evaporation, and pressure changes. Irregular pools require an appropriate geometric volume estimate before calculating filling time.
Try your own values
Use the pool fill time calculator to test your inputs. Save two scenarios to compare results, or copy an input link to revisit your calculation.
For a shorter explanation, read the direct answer. Compare the underlying quantities in the comparison.
