How to Calculate Water Tank Pump Capacity for Your Home

Sizing a pump to fill your overhead tank correctly means it fills in a reasonable time without wasting energy or cycling constantly. This guide shows the simple calculation with real examples.

1. The Two Numbers You Need

• Flow rate: How fast the pump moves water (litres per minute)
• Head: How high it must lift the water (metres)

2. Calculate Required Flow Rate

Decide how quickly you want the tank filled. Flow rate = Tank capacity ÷ Desired fill time. Example: a 1,000-litre tank you want filled in 20 minutes needs 50 litres/minute.

3. Calculate Head

Head = height from the pump/sump water level to the tank inlet + pipe friction + safety margin. For a typical 2-storey home: about 8m lift + 2m friction = 10m head.

4. Worked Example

1,000L tank, fill in 20 min (50 LPM), 2-storey home (10m head). A 1 HP monoblock or 1 HP submersible comfortably delivers 50+ LPM at 10m — the right choice.

5. Avoid These Mistakes

• Oversizing so the tank fills in 5 minutes — the pump short-cycles and wears out
• Undersizing the delivery pipe — chokes the flow regardless of pump size
• Ignoring head — a high-flow pump with low head rating will not reach an upper tank

Give us your tank size, floors, and water source and we will calculate and supply the correctly-sized pump. Contact us or send a pump inquiry for free sizing guidance.