How to Calculate Drip Line Length and Run Time

In any Drip Line system, it is important that you calculate the amount of Pipe required and how long your system needs to be running for. Depending on which dripline you are selecting, the spacing and litre per hour output will all have an effect on the run time.

Make sure you check your water flow rate and pressure to ensure there is enough water to run your irrigation system.

How to Calculate Your Flow Rate and Water Pressure

Follow the calculation summary below to work out how to calculate the run time of your Drip Line. You can also view the working example tabs as a guide, created for you to reference when calculating these figures. Alternatively, you can refer to the 'suggested run time' table for an approximate watering time, based on what you are watering.

Drip Line Calculation

1. Area x Average water loss = Required Litres per day

2. (Dripline length in metres ÷ Dripper spacing in metres) x Litre output = L/h (Litres per hour)

3. L/h ÷ 60 = L/m (Litres per minute)

4. Required Litres per day ÷ L/m = Run time

In this example, the raised bed measures: 4m x 2m = 8m².

• An average plant needs 4 - 5mm (4.5mm) of water a day to replace the average water loss on a dry day.
• We will use 1.8 L/h - 30cm spacing 13/14mm Drip Line. Each dripper outlet soaks into a cone shape of 30cm either side of the outlet, ensuring water is supplied to the root of the plant.

Raised bed watering requirements per day:

We calculate the size of the raised bed (metre squared) by how much water the plant will lose on a dry day.

8m² (size of the raised bed) x 4.5mm (Water per day needed for plants) = 36.

This bed needs 36 litres of water per day.

Setting Up Your Drip Line

We recommend using elbow and tee connectors to create a grid formation. By laying the Drip Line pipe in rows and the same distance apart as the spacing, you can ensure an adequate wetting pattern for plants, e.g. if your dripper spacing is 30cm then the space between rows of pipe line should be 30cm. Secure the pipe in place using stakes and make sure you use an end piece to close the system.

Continuing from our example above, using 16m of Drip Line with a spacing of 30cm (0.3m) between each dripper, here is the calculation summary:

• (16m ÷ 0.3m) x 1.8 L/h = 96 L/h.
• 96 L/h ÷ 60 = 1.6 Litres per Minute (L/m).
• Run Time of Drip Line = 36L ÷ 1.6 L/m = 22.5 Minutes.
• Run Time = 22.5 Minutes.

Suggested Run Times for Drip Line

* The table above is a suggestion only, based on one run time on an average summer day. You may wish to adjust frequency and duration through the season, depending on the climate.

** To see suggested run time for Trees, please refer to the Working Example.

In this example, we are using 4mm Drip Line that releases 2 L/h at 15cm intervals.

To calculate the length of the Drip Line to surround your tree, we use a different calculation using the circumference of the tree canopy. Measure the distance from tree trunk to the edge of the canopy. The tree canopy is known as the "Drip Line" or the "critical root zone". This area and beyond is the most active water absorption area of a tree. Watering too close to the trunk can cause root rot.

To calculate the length of the Drip Line needed, we use the following calculation:
• (2 x 3.14) x distance (radius) from the trunk to the edge of the tree canopy.

Tree Circle Watering Requirements Per Day:

The general reference for established trees is 45L of water for every 2.5cm of the tree's diameter. If our tree radius is 1.5m:

• (2 x 3.14) x 1.5 = 9.42.
• 9.42m of Drip Line - use 10m of Drip Line to ensure the edge of the tree canopy and critical root zone received adequate water supply.
• 10m of Drip Line will give 66 drippers in total.
• 66 x 2 L/h = 132 L/h.
• 132 L/h ÷ 60 = 2.2 L/m.

Our tree will need 90L of water based on the guide for established trees.

• Run Time = 90 ÷ 2.2 = 40 Minutes.

To encourage a deeper and wider root zone it is important to regularly water in the early years. During hot and dry weather, new trees may need water up to three times a week to ensure the root ball doesn't dry out.

For more established trees, we would recommend watering for longer durations and less frequently to encourage deeper root growth; follow the wetting pattern guide below.

Testing Soil Water Distribution and Wetting Patterns

Depending on the soil type and climate, you may wish to check how much water is being distributed. Based on the method below, you might need to adjust the watering times accordingly.

You should be looking for a wet spot of 8 - 10cm in diameter from the drip emitter. You can test the wetting pattern by running the system for 30 minutes. Stop the water flow for a further 30 minutes and dig into the soil below the emitter and see how far the water has moved both vertically and horizontally. Ideally, you should have a 30cm wetting area around the emitter.

Now that you know how to set your system up, it's important to know which Drip Line you need and what unique features to look out for, including the internal diameter and whether it's pressure-compensating and/or anti-siphon. Click Here for our guide on the different types of Drip Line.

	4mm Micro-drip 2 L/h	4mm Micro-drip 2 L/h	14mm 0.85 L/h	14mm 1.6 L/h	14mm 1.6 L/h	14mm 1.8 L/h	14mm 2.0 L/h	14mm 2.0 L/h	14mm 2.1 L/h
	15cm spacing	30cm spacing	30cm spacing	30cm spacing	30cm spacing	30cm spacing	33cm spacing	50cm spacing	30cm spacing
Grass/Lawn			16 Mins	16 Mins	16 Mins	15 Mins	14 Mins	23 Mins	13 Mins
Raised Bed	5 - 10 Mins	20 - 25 Mins	50 Mins	13 Mins	25 Mins	23 Mins	22 Mins		19 Mins
Shrubs	5 - 10 Mins	20 - 25 Mins	50 Mins	13 Mins	25 Mins	23 Mins	22 Mins		19 Mins
Hedges/Borders	5 - 10 Mins	20 - 25 Mins	50 Mins	13 Mins	25 Mins	23 Mins	22 Mins	34 Mins	19 Mins
Hedges/Borders	5 - 10 Mins	20 - 25 Mins	50 Mins	13 Mins	25 Mins	23 Mins	22 Mins	34 Mins	19 Mins
Trees	8 - 10 Mins	15 Mins	38 Mins	9 Mins	20 Mins	18 Mins	17.5 Mins		15 Mins

Further Drip Line Information

For further information on how to install a drip line garden watering system, including which drip line to use and how to install and maintain a drip line system, read our how-to guides.