Flow rate: how much, how fast
Measure how much water moves each minute — the number every pump is judged by.
⏱ 4 min
- Everyday comparisonStep 1 of 5
Filling a bucket
You fill a bucket with a garden hose. Turn the tap a little: it takes ages. Turn it fully open: it fills fast.
How much water arrives each minute is called the . It is the first thing anyone asks about a pump: “How much can it move?”
- Try itStep 2 of 5
Open the tap
Drag the tap handle to change how much water flows. The meter shows the flow rate in litres per minute (L/min).
The clock shows how long it takes to fill the 10-litre bucket.
Challenge: Try to fill the bucket in about 20 seconds. What flow rate do you need? (Hint: 10 litres in ⅓ of a minute.)
- ExplainedStep 3 of 5
Speed × size of the pipe
Flow rate depends on two things: how fast the water moves, and how big the pipe is.
A slow river can move far more water than a fast garden hose, simply because it is so wide. Engineers write it as Q = v × A — flow = × .
- ExplainedStep 4 of 5
Units you will meet
Small pumps are usually rated in L/min (a kitchen tap gives roughly 6–12 L/min).
Big pumps are rated in m³/h — cubic metres per hour. One cubic metre is 1000 litres, about five bathtubs. 1 m³/h is roughly 16.7 L/min.
- The impeller connectionStep 5 of 5
On every pump label
Every pump has a label or data sheet that says how much it can move. Soon you will learn that the flow rate changes depending on how hard the pump has to push. That relationship is the heart of pump engineering.
📌 Remember this
Flow rate (Q) is how much fluid passes each second or minute. It equals the fluid’s speed times the size of the pipe.