Farm Irrigation Cost Calculator NZ

This works out what irrigation actually costs to run, starting from the pump physics rather than from a rule of thumb. Give it the flow rate, the total head the pump is working against and the efficiency of the pump and motor, and it returns the kilowatts being drawn, the cost an hour, the cost to cover a hectare and, most usefully, the cost per millimetre applied. That last unit is the one decisions get made in: nobody decides to run the pump for six hours, they decide to put 10 millimetres on a paddock, and pricing that directly is what lets one system be compared with another. The physics is exact and there is nothing to argue about in it, because lifting a litre of water a metre takes a fixed amount of energy. All the variation lives in two places. The first is efficiency, and it is not a detail: a worn pump running at 55 percent where it should be at 75 costs about a third more for precisely the same water delivered. The second is head, where friction loss in the mainline is the component most often forgotten, which is how an undersized pipe ends up costing money every hour the pump runs rather than once at installation.

Calculate.co.nz is proud to be partnered with Health Based Building, a leader in sustainable and health-conscious building innovation. With over a century of experience, they develop high-performance systems like Foreverbreathe Specification, Magnum Board, and Foreverbreathe Paints to support energy-efficient, non-toxic living environments. Their commitment to healthier homes aligns with our belief that informed choices lead to better outcomes for Kiwi households.
Calculate.co.nz partner: Health Based Building
L/s
m
%
$
/kWh
ha
mm
$0.59
a hectare for every millimetre applied
Power drawn45.4 kW
Cost an hour$9.54
Hours for that depth37.0 hrs
Cost for the round$353.16

At 55 percent efficiency rather than 70, the same round would cost $449.48, which is $96.32 more for water the paddock cannot tell apart. Pumping energy only. Labour, maintenance, capital, consent charges and any fixed line charges sit outside this.

The hydraulic arithmetic here is physics, not a rate: power equals flow times head times gravity, divided by efficiency, using 9.81 metres per second squared. No efficiency, electricity price or system figure is supplied as a standard, because all three are yours.

How it works

Hydraulic power in kilowatts is the flow in litres a second multiplied by the total head in metres and by gravity at 9.81, divided by a thousand. Dividing by the efficiency gives the electrical power actually drawn, since the difference between the two is what the pump and motor lose as heat and noise. Cost an hour is that power multiplied by your electricity price. The volume needed for a round is the area multiplied by the depth, using the exact conversion that a millimetre over a hectare is 10,000 litres, and dividing by the flow gives the hours. Multiply out and you have the cost of the round and the cost per millimetre per hectare.

What efficiency is worth

Efficiency divides, so it moves the answer more than most people expect. Dropping from 75 percent to 55 raises the power drawn by more than a third for exactly the same water delivered, and that shows up on every invoice for the rest of the season. It is also the one figure on this page that can quietly change without anyone noticing, because a pump wears gradually and nothing about the water coming out of the sprinkler announces it. If you have never had the system tested, the efficiency you assume here is a guess and probably a generous one.

Worked example

A pump moving 45 litres a second against 72 metres of total head at 70 percent efficiency draws 45.4 kilowatts. At 21 cents a kilowatt hour that is $9.54 an hour. Putting 10 millimetres on 60 hectares needs 6,000,000 litres, which at 45 litres a second takes 37.0 hours and costs $353.16, or $0.59 a hectare for each millimetre applied. If the pump were actually running at 55 percent rather than 70, the same round would cost $449.48, which is $96.32 more for water the paddock cannot tell apart.

Related calculators

Data sources: the hydraulic power calculation is physics rather than a published rate, using standard gravity at 9.81 metres per second squared, and the conversion that one millimetre over one hectare is exactly 10,000 litres. Efficiency, electricity price and system figures are all yours to enter.

Frequently asked questions

How do you calculate irrigation pumping cost?

Power in kilowatts is the flow in litres a second multiplied by the total head in metres and by gravity, divided by the pump and motor efficiency. Multiply that by the hours run and by your electricity price and you have the cost. The physics part is exact: lifting one litre one metre takes a fixed amount of energy. Efficiency is where the real variation sits, and a worn pump running at 55 percent instead of 75 costs a third more for exactly the same water.

What is total head?

The full pressure the pump has to work against, expressed in metres. It is the vertical lift from the water source to the outlet, plus the operating pressure the sprinklers need, plus friction losses in the pipework. Friction is the part most often left out, and on a long mainline it can be a substantial share of the total, which is why an undersized pipe costs money every hour the pump runs rather than only once at installation.

Why express irrigation cost per millimetre?

Because it is the unit the decision is actually made in. You do not decide to run the pump for six hours, you decide to put 10 millimetres on a paddock, and cost per millimetre per hectare lets that decision be priced directly. It also makes systems comparable: a pivot and a travelling irrigator applying the same depth to the same area can differ substantially once the pumping cost per millimetre is worked out.