How to choose the right pipe size

Pipe size is the single most common thing people get wrong, usually by buying whatever the shop has in stock. The cost of getting it wrong is not obvious on day one — it shows up as weak flow at the far end of the field, or as money spent on pipe thicker than the job needed.

Bore is not the same as length

Two numbers describe a pipe and they are routinely confused. The bore (or size) is the internal diameter — 20mm, 32mm, 63mm, or in inch terms 3/4", 1", 2". The length is how much pipe is on the coil — 30 metres, 100 metres, 150 metres.

When someone says "3 inch pipe", they mean bore. When they say "100 metre pipe", they mean coil length. A product is only fully specified when you state both.

Bigger bore, less friction

Water rubbing against the pipe wall loses pressure. The longer the run and the narrower the bore, the more pressure you lose before the water reaches the far end.

This is why a line that works fine at 30 metres goes weak at 100 metres on the same pump. The pump did not change; the friction did. Widening the bore one step is usually cheaper than upgrading the pump.

A practical starting point

Match the mainline to your pump outlet, then step down for laterals. If your borewell delivers through a 2" outlet, running a 3/4" mainline throttles it immediately, no matter how good the pipe is.

For long runs, err one size up. The extra cost is a one-time expense; the pressure loss is permanent.

These are rules of thumb, not a design. Flow rate, static head, pump curve and layout all matter, and a field of any size deserves a proper calculation rather than a guess. Send us your pump details and field dimensions on WhatsApp and we will work it through with you.