Quick answer: to size a borehole pump you need three numbers. First, how much water you use in a day. Second, the flow, which is that daily amount divided by the hours you can pump. Third, the total head, which is how high the pump must push the water, from the pumping water level up to the top of your tank, plus friction in the pipes. Flow and head together decide the pump. Horsepower comes last.
The calculator below works through each step and shows its working, so you can check a quote or talk to an installer with confidence.
Borehole pump sizing calculator
Change any number and the result updates. Leave a box at 0 if it does not apply.
A planning estimate, not a pump specification. The final pump is chosen from the manufacturer’s pump curve and your test pumping results. For a quick horsepower and tank answer, use our pump and tank size calculator.
Step 1: Work Out Your Daily Water Demand
Everything starts with how much water you use in a day. Count everyone and everything that drinks from the borehole.
| User | Typical daily use | Figure used in the calculator |
|---|---|---|
| Person at home | 50 to 100 litres | 75 L, or choose 50 or 100 |
| Dairy cow (milking) | 30 to 80 litres, more in hot weather | 60 L |
| Beef cattle | 35 to 60 litres | 45 L |
| Goat or sheep | 5 to 20 litres | 10 L |
| Pig | 15 to 25 litres | 20 L |
| Poultry | 40 to 50 litres per 100 birds | 0.5 L per bird |
Livestock ranges are from Infonet Biovision’s livestock water guide. Animals drink more in the dry season, so size for the hottest months. For crops, our irrigation water requirement calculator gives the litres per day to enter as other use.
Step 2: Turn Daily Demand Into Flow
Flow is how fast the pump must deliver water. Divide your daily demand by the hours you can pump.
Flow (m³/h) = daily demand in litres ÷ 1,000 ÷ pumping hours
Pumping hours matter a lot. A solar pump without batteries works only in good sunlight, so plan on about six hours a day. A grid pump can run longer, which means a smaller flow and often a smaller pump. This is why a tank is part of every good design: it stores the day’s water so the pump does not have to match your peak use. Read why your borehole needs a water tower.
Your flow must also stay within what the borehole can safely give. That figure comes from the test pumping report. If your flow is close to the tested yield, pump for longer at a lower rate.
Step 3: Work Out the Total Head
Head is the height, in metres, that the pump must push water. It has three parts.
- Lift from the pumping water level. Use the level while the pump is running, not the resting level. Water drops when you pump, and the test pumping report gives this figure.
- Height to the tank. Add the tank stand height and any rise in the ground between the borehole and the tank.
- Friction. Water loses energy rubbing against the pipe. Long runs, narrow pipes and high flow all add friction. The calculator uses the standard Hazen Williams formula for plastic pipe, plus 10% for bends and valves.
The pump itself hangs below the pumping water level so it never runs dry. The calculator assumes about 10 metres of extra pipe for that when it works out friction.
Step 4: From Flow and Head to Pump Power
The power needed to lift water is a standard calculation:
Water power (kW) = flow (m³/h) × total head (m) ÷ 367
No pump turns all of its electricity into lifting water. Small submersible pumps and motors together are often only 40% to 60% efficient, so the motor must be larger than the water power. The calculator divides by those efficiencies and then rounds up to the next common motor size.
One kilowatt is about 1.34 horsepower, so a 0.75 kW pump is roughly a 1 HP pump.
Two Worked Examples
| Step | Family home with a few cows | Farm with irrigation |
|---|---|---|
| Water users | 6 people, 10 dairy cows, 20 goats | 10 people, 20 dairy cows, 40,000 L of drip irrigation |
| Daily demand | 1,250 L | 41,950 L |
| Pumping hours | 6 (solar) | 6 (solar) |
| Flow | 0.21 m³/h | 6.99 m³/h |
| Pumping water level | 80 m | 60 m |
| Tank and ground rise | 8 m | 8 m |
| Pipe | 50 m of 1 inch | 200 m of 1½ inch |
| Friction | 0.1 m | 19.2 m |
| Total head | 90 m | 89 m |
| Motor power needed | 0.09 to 0.13 kW | 2.83 to 4.25 kW |
| Pump size to discuss | 0.37 kW, the smallest common size | 5.5 kW |
The two sites have almost the same head, yet one needs a pump fifteen times larger. Flow makes the difference. Notice too that friction added almost 20 metres on the farm. A 2 inch pipe would cut that sharply and may allow a smaller pump.
Solar or Grid?
Solar suits most Kenyan boreholes because sunshine is strong and running costs are close to zero once the system is in. The trade off is fewer pumping hours, which pushes the flow and pump size up. A common rule of thumb is a solar array of about 1.3 to 1.5 times the pump rating.
Grid power lets the pump run longer, often at night into a tank, so a smaller pump can do the same job. Many sites combine both. Our guide to solar borehole pump installation in Kenya covers the choice in detail.
Common Pump Sizing Mistakes
- Buying by horsepower alone. Two 1 HP pumps can deliver very different flows at your head. Check the pump curve at your total head.
- Using the resting water level. The level drops while pumping. Size from the pumping water level in the test report.
- Oversizing. A pump that is too big empties the borehole faster than it refills, trips on dry run and wears out early.
- Skimping on pipe. A narrow rising main adds friction every day the pump runs.
For the types of pump available, read our guide to borehole pumps, and for everything that goes into a finished system, see borehole equipping.
Frequently Asked Questions
What size pump do I need for a 100 metre borehole?
Depth alone does not decide it. What matters is the pumping water level, which is often well above the bottom of the borehole, plus your daily demand and pumping hours. A home using about 1,000 litres a day may need only the smallest common pump, while a farm with irrigation may need several kilowatts.
How do I calculate total head for a borehole pump?
Add the pumping water level, the height of the tank and any ground rise to the tank, and the friction loss in the pipe. A small allowance at the tank inlet is usually added too.
How many solar panels does a borehole pump need?
A common rule of thumb is a solar array of about 1.3 to 1.5 times the pump rating. The final number depends on the pump, its controller and the sunshine at your site.
Can a pump be too big for a borehole?
Yes. If the pump draws water faster than the borehole refills, the level falls to the pump, which then trips or runs dry. Keep the flow within the safe yield from your test pumping report.
Is horsepower the same as kilowatts?
They measure the same thing in different units. One kilowatt is about 1.34 horsepower, so a 1.1 kW pump is roughly 1.5 HP.
Get Your Pump Sized Properly
We size and install complete borehole pump systems across Kenya, using your test pumping results. Call or WhatsApp Bonvic Drilling on 0727 666 444, or see our borehole pump installation service.
