Convert flow rates and use time-volume checks to catch unit errors.
Core idea
There are 60 seconds in one minute. Convert litres per second to litres per minute by multiplying by 60. Convert litres per minute to litres per second by dividing by 60. Keep flow rate separate from the total volume collected.
What to recognise
- 0.2 L/s equals 12 L/min.
- 18 L/min equals 0.3 L/s.
- Volume equals flow rate multiplied by time when the flow is steady.
- Convert time into the unit used by the flow rate before multiplying.
- Use a measured collection time long enough to reduce timing error where practical.
Apply it
If a vessel collects 10 litres in 40 seconds, flow is 10 ÷ 40 = 0.25 L/s, then 0.25 × 60 = 15 L/min. Sense-check by asking whether 15 litres in a full minute agrees with 10 litres in two-thirds of a minute.
Limits
Real flow changes with pressure, valve position and simultaneous demand from other outlets. Converting units tells you nothing about pipe capacity or compliance. Say whether a figure is a measured, design or required flow, and compare like with like.
Flow rate from velocity
Flow rate is the bore's cross-sectional area multiplied by the average velocity of the water: Q = A × v. With the area in m² and the velocity in m/s, Q comes out in m³/s; multiply by 1000 for litres per second. A bore of 0.0004 m² carrying water at 0.5 m/s passes 0.0004 × 0.5 = 0.0002 m³/s, which is 0.2 L/s or 12 L/min. For the same flow, a narrower bore means a faster velocity.