Drip Irrigation Pump Calculator: A Worked Guide

Use the drip irrigation pump calculator to turn zone flow, emitter pressure, lift and pipe length into total head and power. In the live worked example, 600 L/h at 1 bar with 3 m of lift and 50 m of pipe needs 15.7 m of total head and about 51 W.

The rest of this guide walks through each input, each formula and each step of that example. The power figure uses 50 percent efficiency, a figure that appears only inside that example.

What the drip irrigation pump calculator gives you

The calculator takes the flow of your largest zone, the pressure your drip line needs, the lift from the water surface to the highest emitter, and your supply pipe length with a friction allowance. It gives total head and power. Total head is the resistance the pump works against, in metres or feet of water. Power is the power the pump needs to deliver that flow at that head at the efficiency you enter.

Use total head and flow together. The result is a pair, flow at total head, and that pair is what you match to a pump curve.

The calculator works from a tank or a well. It does not give a cost, a brand, a model, a pump curve, a run time, an emitter count or a zone count. It does not set a default efficiency.

The 5 inputs in order

Follow the order on the live page when you gather your numbers. Each input has one job, and a wrong value in any one of them moves the total head or the power result.

1. Flow of the largest zone

Enter the flow of the largest zone, in litres per hour. Size the pump for the largest zone, because that zone asks the pump for the most water at one time. If you are unsure of the flow, check it with the drip flow rate calculator before you start.

2. Pressure the drip line needs

Enter the pressure the drip line needs, in bar. This is the pressure at the emitters, not the pressure at the pump. The calculator turns this pressure into pressure head, using 10.2 m of head for each bar.

3. Height from the water surface to the highest emitter

Enter the lift, in metres. Lift is the vertical height from the water surface in the tank or well to the highest emitter in the zone. A pipe that runs uphill and then downhill still asks the pump to lift water to the highest point.

4. Supply pipe length and a friction allowance

Enter the supply pipe length, in metres, and a friction allowance as a percentage. The calculator finds friction by multiplying pipe length by the loss percentage. In the worked example, 50 m of pipe at 5 percent loss gives 2.5 m of friction head. Friction here is an allowance, not a measured value from a pipe diameter table, because the calculator gives no pipe diameter friction table.

5. Pick a pump with a margin

Pick a pump whose curve gives your flow at the head shown, with a margin. In the worked example the choice is a pump giving at least 720 L/h at 19 m, against a need of 600 L/h at 15.7 m. That choice is about 20 percent more flow and about 20 percent more head, worked out from the page figures. The page does not name a margin rule, so treat the 20 percent figure as arithmetic from the example only.

Formula 1: total head

Total head has three parts, and the calculator adds them in one simple sum. First, pressure head equals pressure times 10.2, with pressure in bar and the result in metres. Second, friction equals pipe length times loss percent, with pipe length in metres and the result in metres. Third, total head equals lift plus pressure head plus friction, all in metres.

In the worked example, pressure head is 10.2 m, lift is 3 m and friction is 2.5 m, so pressure head alone is more than lift and friction together. Total head is also called total dynamic head on the live page, and the name means the total resistance the pump works against, with height, pressure and friction combined.

Formula 2: power

Power uses flow, head and efficiency in one formula. Power equals 9.81 times flow in litres per second times head in metres divided by efficiency. Flow must be in litres per second for this formula, so convert litres per hour by dividing by 3600. Efficiency is entered as a decimal, so 50 percent efficiency is 0.50 in the formula.

At 50 percent efficiency, about half the power in is lost before it reaches the water, and the formula divides by 0.50 to show that. The power result is in watts. It is not a running cost, because the calculator gives no run time and no price.

Worked example in full, metric

Here is the worked example from the live page, with every step recomputed. The inputs are 600 L/h of flow, 1 bar of emitter pressure, 3 m of lift, and 50 m of pipe at 5 percent loss. The efficiency used is 50 percent.

Step	Calculation	Result
Pressure head	1 bar times 10.2	10.2 m
Friction	50 m times 5 percent	2.5 m
Total head	3 m plus 10.2 m plus 2.5 m	15.7 m
Flow in L per s	600 divided by 3600	0.1667 L per s
Power	9.81 times 0.1667 times 15.7 divided by 0.50	51.3 W
Pump choice	At least 720 L per h at 19 m	Margin over need

Steps 1 to 3 give total head. One bar times 10.2 gives 10.2 m of pressure head. Fifty metres times 5 percent gives 2.5 m of friction. Three metres of lift plus 10.2 m plus 2.5 m gives 15.7 m.

Steps 4 and 5 give power. Six hundred litres per hour divided by 3600 gives 0.1667 litres per second. Take 9.81 times 0.1667 times 15.7, which gives 25.67, and divide by 0.50, which gives 51.3 W, stated on the live page as about 51 W.

Step 6 is the pump choice: at least 720 L/h at 19 m. Seven hundred and twenty divided by 600 gives 1.2, which is 20 percent more flow. Fifteen point seven times 1.2 gives 18.84 m, rounded to 19 m.

Imperial figures as rounded equivalents

The live page gives no imperial worked example, so this section does not convert the metric example lift and pipe length into feet. It uses only the conversion factors the page states, labelled as rounded equivalents, not exact conversions.

One bar of pressure equals about 10.2 m of head, which the page also states as about 33.5 ft of head. One psi equals 2.31 ft of head. So 10 psi times 2.31 gives 23.1 ft of head, and 20 psi times 2.31 gives 46.2 ft of head. Gravity gives only about 0.1 bar per metre of height, which the page also states as about 1.4 psi per 3.3 ft of height.

How to read a pump curve and choose with a margin

A pump curve is a chart from the pump maker that shows flow against head. Find your total head on the head axis, then read the flow the pump gives at that head. A pump that lists a high maximum head may give very little flow at that head, and a pump that lists a high maximum flow may give that flow only at a low head. The live page warns to check flow at your head, not maximum head.

Choose a pump that gives at least your flow at at least your head, with a margin. In the worked example that margin lands at 720 L/h at 19 m for a need of 600 L/h at 15.7 m. A margin gives room for friction above the allowance. If the curve shows your flow only at a head below your total head, that pump is too small. Either pick a pump that meets flow at your head, or shorten the pipe run, reduce the lift, or split the zone so the largest zone flow falls.

Can a rain barrel run drip irrigation without a pump

Gravity from a rain barrel gives only about 0.1 bar per metre of height, which the page also states as about 1.4 psi per 3.3 ft of height. That is low pressure for most drip lines, which is why the live page says to use low pressure drip kits or a small pump when the source is a rain barrel.

If you plan a rain barrel system, work out the height from the water surface to the highest emitter first, then work out the gravity pressure from that height. If gravity pressure falls short, a small pump that meets your flow at your total head is the practical route. The rain barrel calculator on this site can help with the water volume side of that plan.

What the calculator does not give

The calculator gives flow, total head and power, and it does not give anything else. It gives no cost or price, no pump brand or model, and no pump curve data. It gives no default efficiency, and 50 percent is used only inside the worked example. It gives no imperial worked example, no pipe diameter friction table, and no figure for how much gravity head a rain barrel gives beyond 0.1 bar per metre.

It also gives no run time, no emitter count, no emitter spacing, no tubing length, no fitting count and no zone count formula. If you need emitter numbers, use the drip emitter calculator. If you need a full layout, use the drip irrigation planner. Use the calculator for what it gives, and check the pump curve before you buy.

Frequently asked questions

Q: What size pump do I need for drip irrigation?
A: Choose a pump that delivers your zone flow at your total head. In the worked example that means at least 720 L/h at 19 m for a need of 600 L/h at 15.7 m.

Q: What is total dynamic head?
A: Total dynamic head is the total resistance the pump works against, in metres or feet of water, with height, pressure and friction combined.

Q: Can a rain barrel run drip irrigation without a pump?
A: Gravity gives only about 0.1 bar, or 1.4 psi, per metre, or 3.3 ft, of height, so a raised barrel alone gives low pressure. Use low pressure drip kits or a small pump.

Q: How do I convert psi to feet of head?
A: Multiply psi by 2.31 to get feet of water. For example, 10 psi times 2.31 gives 23.1 ft of head.

Q: What flow should I enter in the drip irrigation pump calculator?
A: Enter the flow of the largest zone, in litres per hour, and check that flow with the drip flow rate calculator if you are unsure of it.