Calibration: flow rate, litres and rain gauge

One number decides how much water your plants get, and it is the flow rate calibration. This page shows how to get it right, and how to set the two smaller numbers that go with it. The menu names are the ones in Home Assistant: Settings, Devices and services, ZoneFlow, the zone, then Configure.

What calibration means

ZoneFlow works out how much water each plant needs, then turns that into minutes with the valve open. To do that it needs to know how much water ends up on the ground every minute. Imagine the valve is open for one minute. How deep a layer of water do your drippers or sprinklers put on the soil? Gardeners measure that depth in millimetres, or inches. A typical drip line puts about a quarter of a millimetre per minute. ZoneFlow shows it as Emitter Flow Rate Calibration.

Too low a number: ZoneFlow thinks the system is weak, runs the valve longer than needed, and overwaters.
Too high a number: ZoneFlow thinks the system is strong, runs the valve shorter than needed, and underwaters.

Until you set it, ZoneFlow uses a typical value and reminds you in Home Assistant's Repairs list. It is the one setting that really must be right.

Pick your method

All three methods are under Configure → Flow rate.

You have drippers or sprinklers with the flow printed on the packaging: calculate it from the emitters. Good, if the packaging numbers are true for your pressure.
You have a bucket, a barrel or a water meter: measure it by the litres a service run gave. Best, and needs no special hardware.
You have a flow meter on the zone: measure it with the flow meter. Best, and fully automatic.

Method 1: calculate it from your emitters

You need three numbers:

How many emitters (drippers, sprinkler heads) the zone's valve feeds.
How much one emitter gives, in litres per hour (or gallons per hour). It is printed on the emitter or its packaging, for example 2 L/h.
The area they water, in square metres (or square feet). For drippers at single plants, add up the small wet patches around each plant, not the whole bed.

Open Configure → Flow rate: work it out from the emitters, enter the three numbers, and ZoneFlow does the maths and sets the calibration.

For example, 50 drippers of 2 L/h each water 20 m². That is 100 L per hour on 20 m², which is about 0.08 mm per minute.

Packaging numbers are for ideal pressure. A long line, a weak pump or a clogged filter gives less. If you can, check with Method 2.

Method 2: measure it with a bucket (recommended)

You need nothing except something to catch water.

Press Service Run 15 min on the zone. It runs the valve for 15 minutes and does not count as a watering. A longer run is more accurate. 5 or 10 minutes also work.
Catch the water that comes out: a bucket or barrel under the emitters, or read the difference on a water meter before and after.
Open Configure → Flow rate: measure it by the litres a service run gave.
Enter the minutes the valve was open, the litres you caught, and the area the water falls on.

ZoneFlow works out the calibration for you. For example, 15 minutes gave 36 litres on 10 m². 36 litres divided by 10 m² divided by 15 minutes is 0.24 mm per minute.

There is a longer walk-through of the jug method for drip and the cans method for sprinklers in How to measure your irrigation flow rate with a bucket.

Method 3: let a flow meter do it

If the zone has a flow meter that reports litres, such as a pulse meter, choose Configure → Flow rate: measure it with the flow meter, enter the area, and ZoneFlow runs the valve for 10 minutes, reads the meter and sets the calibration. You get a message on your phone with the result.

The meter must measure only this zone's water while it runs. If it also counts other zones, the number will be too high.

"The area they water": the most common mix-up

The area is where the water actually lands, not the size of the garden.

Drippers at each plant: add up the wet circles. Ten tomato plants with a 30 cm wet patch each is only about 0.7 m², not the whole bed.
Sprinklers and soaker hoses: the area they cover.
Not sure? Run a service run, dig a few centimetres down and see how wide the wet patch is.

A wrong area is the most common reason a calibration feels wrong. Too big an area makes ZoneFlow think the system is weaker than it is.

Zone Flow: litres, not depth

ZoneFlow can also show how many litres each zone uses: the last watering, the last 30 days and the year so far. For that it needs a second number, Zone Flow, which is how many litres per minute the whole valve gives. This needs ZoneFlow 1.6.5 or newer.

Method 1 and Method 2 set it for you automatically.
Or enter it yourself under Configure → Zone flow: the number of heads and the flow of one head. Drippers are usually given per hour, sprinklers per minute.
With a flow meter, ZoneFlow uses the meter's real litres instead.

Zone Flow is only used to show litres. It never changes when or how long a zone waters. Leave it at 0 if you do not need litres.

Calibrating the rain gauge

This is only needed if your rain gauge is a tipping bucket that counts tips.

Each tip of the bucket is a small amount of rain, usually 0.2 mm or 0.3 mm. Some are 0.254 mm, a hundredth of an inch. Find the number in the gauge's manual, or catch it yourself: slowly pour a known amount of water through the gauge and count the tips. Set it on the zone's device page as Rain Gauge mm per Tip.

If your weather station already reports a rain total, such as Ecowitt, Ambient Weather or Davis, you do not need this. Choose Rain total as the sensor type instead. See Rain gauges and weather stations.

Drippers of different sizes on one valve

ZoneFlow can only use one number per valve. If the heads on a valve are different, some strong and some weak, the calibration is the average. Plants on the weaker heads get less water than the number says.

For the most accurate result, put each type of emitter on its own valve, as its own zone.

How to check that it is right

Water a zone and look at Last Water Delivered (Estimate), the depth ZoneFlow believes it put on.
Dig a few centimetres down a few hours later. The soil should be damp to about the depth the plant's roots reach, not soaked and not dry.
Too wet? The real flow is higher than the calibration. Too dry? It is lower. Repeat Method 2 to fix it.

When to calibrate again

When you change emitters, add or remove heads, or change the pump.
When the pressure changes, for example a new filter or a longer line.
Once a year, or when plants look different from what ZoneFlow reports. Drippers clog slowly, so a yearly check is cheap insurance.

Quick answers

Which number do I really need? Only the flow rate calibration. Zone Flow (litres) is optional, and the rain gauge number only matters for a tipping bucket.

Metric or imperial? Either. ZoneFlow follows your Home Assistant units, or the zone's own units option, and converts for you. See Metric and imperial units.

I changed it, will my past waterings change? No. They stay as they were recorded. The new number applies from the next watering.

It says the result is out of range. Check the numbers. Usually the area is too small or too big, or litres and minutes are mixed up. The calibration has to be between 0.05 and 2 mm per minute.

Does it matter for a lawn with sprinklers? Yes, the same way. Put a few flat-bottomed cups spread over the lawn, run the zone for 15 minutes, and measure the average depth of water in the cups in millimetres. Divide by 15 and you have the millimetres per minute. Set it with the Emitter Flow Rate Calibration slider on the zone's device page.