What Size Poly Pipe for a Farm Water Line?

The longer the pipe and the more water you push through it, the more pressure you lose to friction. Too small a pipe and the water dribbles out the far end.

1. Work out the flow you need

Add up what has to run at the same time: a trough float valve, a garden tap, a sprinkler. Use litres per minute.

2. Length and height

Measure the pipe length and the height difference. Uphill runs lose pressure to height as well as friction.

3. Friction loss

Friction loss rises quickly with flow and falls quickly with a bigger pipe. Going up one pipe size can cut the loss to around a third or less. The Poly Pipe Size Calculator gives a rough figure.

4. Pressure rating

Poly pipe is sold in pressure classes (PN ratings). Pick a rating above the highest pressure the line will see, including the pump's maximum pressure.

5. Quick summary

• Flow, length and height decide the size.
• Bigger pipe, much less friction.
• Check the pressure rating.
• Ask your irrigation supplier to check long or complex lines.

General information only. Check the maker's instructions, and ask your council about approvals.

← Back to all guides