Underfloor Heating Pipe Calculator
Work out how much PEX/PERT pipe a room needs for water underfloor heating, from the room size, pipe spacing, and the run to the manifold.
Room dimensions
Manifold & buffer
Before you buy
- This is an area-over-spacing estimate, not an exact turn-by-turn layout — it doesn't model the precise geometry of a "serpentine" or "spiral" laying pattern, so leave a sensible buffer for turns.
- Serpentine vs. spiral changes how evenly the floor heats, not the total pipe length this formula gives — pick the pattern for heat distribution, not to save pipe.
- A single loop has a practical maximum length (commonly around 60-100m for 16mm pipe, more for larger diameters) before flow resistance gets too high. A large room usually needs splitting into multiple loops on a multi-port manifold — that's an installer's design decision, not something this calculator does automatically.
How this is calculated
The pipe covering the floor area works out to room area divided by pipe spacing — the standard formula used across underfloor heating calculators. The distance to the manifold is added twice (the pipe runs there and back), and a buffer is added on top for turns and any pipe lost to trimming. Actual usage can run a bit higher for a spiral pattern with tight corner turns — that's exactly what the buffer is for.
Common questions
Why is this an estimate, not an exact figure?
Because the area ÷ spacing formula assumes the pipe perfectly fills the floor in parallel rows — it doesn't account for the exact length used in the turns at each end of a row, which depends on the laying pattern and the room's exact shape. That's a small but real difference, which is what the buffer percentage exists to absorb.
Serpentine or spiral — which should I choose?
Whichever suits your installation — this formula gives the same total length either way, since both cover the same area at the same spacing. The real difference between them is heat distribution: spiral (also called "snail") tends to spread heat more evenly across the floor than a simple back-and-forth serpentine.
What if the calculated loop is too long?
Very long loops build up too much flow resistance, so most systems cap a single loop around 60-100m of 16mm pipe (larger diameters can go further). If your total exceeds that, the room needs to be split into two or more loops feeding into a multi-port manifold — a real installation design decision best made with your system's actual pipe diameter and manifold in mind, not something this calculator decides for you.
Part of Home Improvement Calculators