Calculate tubing length, spacing, and loop layout for any room — free pex radiant floor tubing calculator.
Enter your room's length and width in feet, then select your desired tube spacing (typically 9–12 inches for most climates), maximum loop length, and layout pattern. Hit Calculate PEX Layout to instantly see total tubing needed, number of loops, and a per-loop breakdown table.
The "Extra per Loop" field accounts for the tubing run from the manifold to the floor area and back — typically 5–15 feet depending on where your manifold is located.
Radiant floor heating is one of the most efficient and comfortable ways to heat a home, but getting the PEX layout right before installation saves thousands of dollars in material waste and prevents heating performance problems later.
A 300 sq ft bathroom with 9" tube spacing needs about 400 linear feet of PEX — that's roughly 1.3–1.5 coils of standard 300 ft tube. Underestimate, and you're mid-installation at the plumbing supply store. Overestimate, and you've wasted $80–$120 on tubing you'll never use.
The maximum loop length rule (typically 300 ft for 1/2" PEX, 200 ft for 3/8") exists because longer loops create excessive pressure drop and uneven heat distribution — the far end of a 500-ft loop will be noticeably cooler than the beginning. This calculator automatically splits your floor into correctly-sized loops and tells you exactly how many zones you need on your manifold.
Contractors use 6" spacing in tile floors (high thermal mass), 9–12" in slab-on-grade, and 12" in engineered hardwood installations. The wrong spacing means comfort complaints from the homeowner and possible warranty issues with flooring manufacturers.
The core formula for serpentine layout:
Exact formula: Total PEX (ft) = (Room Area ft² ÷ Spacing ft) + (Loops × Extra ft/loop)
The number of loops = ⌈Total base tubing ÷ Max loop length⌉. Spiral (snail) layouts use approximately the same total footage but with a 5% reduction factor due to tighter corner geometry. Each loop length is then calculated as: base footage ÷ loops + extra, ensuring no single loop exceeds your specified maximum.
For most residential applications, 9–12 inch spacing is the standard. Use 6–9" spacing under tile or stone floors where you want fast heat-up response, and 12" for hardwood or laminate to avoid overheating the flooring. In very cold climates, 6" spacing provides higher heat output per square foot when needed.
For 1/2" PEX tubing (the most common size), keep loops under 300 feet. For 3/8" PEX, stay under 200 feet due to higher pressure drop in the smaller diameter. Exceeding these limits causes the far end of the loop to run significantly cooler, creating uncomfortable hot and cold zones in the floor.
Serpentine (back-and-forth) is easier to install and is the most common pattern. The downside is that one side of the room always has hotter supply water. Spiral/snail layouts alternate hot and return passes side-by-side, giving more even temperature distribution across the floor — better for large open rooms but more complex to install.
Rooms larger than about 150–200 sq ft at 12" spacing will require multiple loops to stay under the maximum loop length. Multiple loops from one room are all controlled by the same thermostat zone — they just connect to adjacent ports on your manifold. This is completely normal and has no effect on comfort.