Question 1

How much pipe do I need to repipe a house?

Accepted Answer

It depends far more on the layout than the square footage — a two-storey with stacked bathrooms uses much less than a sprawling single storey with fixtures at opposite ends. Add up the runs you will actually pull, hot and cold, and this adds the waste for your material.

Question 2

PEX or copper?

Accepted Answer

PEX is faster, cheaper, needs far fewer fittings because it bends round corners, and tolerates freezing better. Copper lasts longer, does not care about UV or rodents, and is what some inspectors and buyers still prefer to see. For a whole-house repipe, most plumbers now reach for PEX.

Question 3

What size pipe should the trunk be?

Accepted Answer

Three-quarter inch for the main trunk in a typical house, with half-inch branches to individual fixtures. Half-inch as a trunk will lose pressure the moment two fixtures run at once, which the calculator warns you about.

Question 4

Why are the fitting counts approximate?

Accepted Answer

Because they depend on the route the pipe takes round joists, corners and obstructions, not on the distance. These are the planning rules of thumb a supply house would use to get you close. Treat them as a shopping list to start from, not a bill of materials.

Question 5

Does this cover drains?

Accepted Answer

No — supply pipe only. Drain, waste and vent piping is sized by fixture units under an entirely different set of rules, and it is the part most likely to need a permit and an inspection.

Question 6

Is my data sent anywhere?

Accepted Answer

Everything is worked out in your browser as you type. Nothing you enter is sent anywhere, stored, or attached to you.

Plumbing pipe calculator