Underfloor heating pipe calculator
Pipe length and number of loops for a wet underfloor heating layout.
Fill in the fields and the result will appear here automatically.
Estimates pipe length from area and spacing separately for main and edge zones. Each zone uses area/spacing; averaging the two spacings can produce a different quantity. Loop count rounds against a chosen length limit, and per-loop length is an average rather than a circuit layout. The calculator does not determine pressure, output or surface temperature.
How it works
Formula and logic
Continuous geometric estimate: R = ((A − E)/s + E/se)(1 + w/100), with A and edge area E in m², spacings s and se in m, 0 ≤ E < A and reserve 0–50%. Loops = ceil(R/chosen maximum length); per loop = R/loop count is an average. Spacings and the limit are positive; inputs are finite. Manifold leads, bends, cutting layout, heat output and hydraulic balancing are not calculated separately.
Example
20 m² at 150 mm with a 4 m² edge zone at 100 mm takes 161.33 m of pipe in two loops.
Fields and units
- Heated area — m²
- Pipe spacing — m
- Maximum loop length — m
- Edge zone area — m²
- Edge zone spacing — m
- Allowance — %
How to use
- — Enter the area where the plan places pipe.
- — Set main spacing and edge area, including 0 if absent.
- — Enter edge spacing and the chosen loop-length limit.
- — Choose your reserve; check manifold leads and bends against the plan separately.
Method and limitations
- Calculation method
- Formula and logic
- Limitation
- This is a geometric quantity calculation within the described model. It does not establish load capacity, safety or project compliance; check design parameters separately.
FAQ
Why is the edge zone laid tighter?
The model lets you set a separate edge spacing but does not require it to be tighter than the main spacing. Select it from the thermal design. Enter edge area 0 when there is no separate zone.
What limits loop length?
Enter a limit from the specific system design. Pressure loss depends on diameter, flow, temperature, material and fittings; dimensions alone do not establish a universal 90–120 m limit. This calculator applies only the chosen length budget.
Should I count the whole room?
Count what you actually heat. Pipe is not usually laid under fitted kitchen units or a bath, and including them buys pipe you will not use.
Does spacing change the heat output?
Spacing changes geometric pipe length per m², but output also depends on water temperature, flow, screed and covering. This calculation cannot give thermal output or guarantee uniform heating.
Is the screed included?
No. Screed volume is a separate calculation from area and thickness.