How to Size a Home Water Pump (HP, Head, Flow) for a Two-Storey Villa

How to size a water pump for a two-storey villa: the HP formula from flow and head, a worked example for a ground tank to a roof tank 12 m up, a bathrooms-to-HP table, and Almadah catalogue prices, VAT-inclusive (29/10/2026).

Short answer: Size a pump in three steps: set the flow you need in litres per minute, add static lift to pipe friction and residual pressure to get total head, then apply: power (kW) = flow x head / (6118 x efficiency). For a ground tank feeding a roof tank 12 m up, the result is about 0.7 HP, so choose at least a 3/4 HP pump and check its curve.

What three numbers determine pump size?

Flow (Q) in litres per minute: the volume the pump must deliver, either to fill the roof tank in an acceptable time or to supply the taps running together.
Total head (H) in metres: the vertical distance from the water level in the ground tank to the roof tank inlet, plus friction loss in pipes and fittings, plus any residual pressure required at the outlet.
Pump efficiency (eta): the share of motor power that ends up in the water. 40% is a reasonable assumption for small domestic pumps; it is a calculation assumption, not a catalogue figure.

The formula:

Shaft power (kW) = flow (L/min) x head (m) / (6118 x efficiency)

Divide the result by 0.746 to convert to HP. The constant 6118 combines the density of water, gravity and the litre and minute unit conversions.

How do I size a pump for a ground tank and a roof tank 12 m above it?

The example: a two-storey villa with a ground tank and a roof tank. The vertical distance from the water level in the ground tank to the roof tank inlet is 12 m.

Step	Calculation	Result
1. Flow	Fill a 2,000 L roof tank in about 30 minutes: 2,000 / 30	65 L/min (rounded)
2. Total head	12 m lift + 3.6 m friction (30% of the lift, a working estimate) + 2 m residual at the float valve	17.6 m, rounded to 18 m
3. Hydraulic power	65 x 18 / 6118	0.19 kW
4. Shaft power	0.19 / 0.40 (efficiency)	0.48 kW
5. 10% safety margin	0.48 x 1.10 / 0.746	0.70 HP
6. Standard size	Next commercial size up	At least 3/4 HP, or 1 HP if the pipe run is long or fittings are many

The 30% friction allowance and the 30-minute fill target are working assumptions for the example, not figures from an official text. For precision, calculate friction from the actual pipe length and diameter: a narrower pipe raises the head you need.

How many HP do I need for each number of bathrooms?

If the pump feeds second-floor taps directly from the ground tank instead of filling a roof tank, the calculation changes, because the pump now works at the instantaneous demand flow. The table assumes: total head of 40 m (about 8 m of lift, 2 bar residual pressure and friction), 15 L/min per bathroom and 10 L/min for the kitchen, 60% of bathrooms (rounded up) in use at peak, 40% efficiency, and a 10% margin.

Bathrooms	Bathrooms at peak	Flow (L/min)	Calculated HP	Suggested size
1	1	25	0.60	3/4 HP
2	2	40	0.96	1 HP
3	2	40	0.96	1 HP
4	3	55	1.33	1.5 HP
5	3	55	1.33	1.5 HP
6	4	70	1.69	2 HP

This is a simplified design estimate and does not replace the calculation of an engineer or licensed plumber. The result changes if the head or the number of taps running together differs. Do not use it for commercial or multi-unit residential buildings.

Is horsepower alone enough to pick a pump from the catalogue?

No. Horsepower is the motor rating; what matters is how many litres the pump delivers at the head you need. Product cards in the catalogue usually state maximum head and maximum flow, and the two never occur together: maximum flow is at near-zero head, and maximum head is at near-zero flow.

Catalogue pump	Rating	Stated on the product card	Price (SAR, VAT-inclusive)
Hyundai HWP0024	1/4 HP, 1 inch	Household pump	163.50
Hyundai HWP001	1/2 HP, 1 inch	Max head 40 m, max flow 40 L/min	277.73
Hyundai HWP0025	1/2 HP, 1 inch	23 m head, 90 L/min flow	398.48
Hyundai HWP003	1 HP, 1 inch	70 m, 65 L/min	422.62

As of 29/10/2026. Applying this to our example (65 L/min at 18 m): the HWP001's maximum flow is 40 L/min, so it falls short. The HWP0025 has a 23 m maximum head and a 90 L/min maximum flow, but at 18 m, close to its maximum head, its real flow will drop well below 90, so ask for its curve. The HWP003 has a 70 m maximum head and a 65 L/min maximum flow; 18 m is far below its maximum head, so it is likely to exceed the required flow, but only the pump curve settles it. A practical rule: pick a pump whose maximum head is clearly above your calculated head, and ask the seller or manufacturer for the flow at your exact head.

What mistakes are common when sizing a pump?

Counting only the height difference: ignoring friction and residual pressure gives a pump that fills slowly or not at all.
Comparing by HP alone: a 1 HP pump may be built for high head, and a larger one for high flow.
Neglecting the suction side: keep the suction pipe short and airtight and the pump close to the ground tank; an air leak on the suction line stops pumping.
Undersized pipe: it raises friction and so the head you need. See PPR pipe sizes for each line in a villa.
Ignoring the electrical load: the pump is a load on its circuit, breaker and cable, so have a licensed electrician check ratings against the Saudi Electrical Code.
No float valve or dry-run protection: running the pump dry damages the motor.

How much do water lifting and booster pumps cost, and what is the median?

Prices in the water lifting and booster pumps category as of 29/10/2026 (including 15% VAT, published and approved products):

Cheapest item: SAR 3.50 (an accessory)
Median price: SAR 845.25
Highest: SAR 25,259.75 (industrial hydraulic equipment, not a household water pump)

The range is wide because the category mixes accessories costing a few riyals with industrial equipment costing thousands, so rely on the median and compare household pumps with each other: in the examples above, SAR 163.50 to 422.62. We do not promise a fixed price; prices change.

Which brands and which product lead this category?

Hyundai leads the named brands in the category, followed by Grundfos and zetalia, with DAB and Al-Zamil also present. The most requested product as of 29/10/2026 is the Hyundai HWP0024 1/4 HP pump. Order volume in this category is still small, so do not treat the ranking as definitive.

FAQ

How many HP does a two-storey villa pump need?

Usually between 3/4 and 2 HP depending on head and number of bathrooms. For a ground tank to a roof tank 12 m up, the example gives about 0.7 HP, so choose at least 3/4 HP.

Is lift height just the height difference?

No. Total head = actual lift + friction loss in pipes and fittings + the residual pressure required at the outlet.

What is the difference between maximum head and maximum flow?

Maximum head is the highest lift the pump can push against with almost no flow; maximum flow is the most it can deliver at near-zero head. Real operation lies between them on the pump curve.

Do I need a pressure tank with the pump?

Usually yes when feeding taps directly, to cut pump cycling and steady the pressure. Details are in the guide to pumps, heaters and filters.

Are the prices VAT-inclusive?

Yes, all prices include 15% VAT, and no tax is added on top of the displayed price.