PEX Pipe Coil Length Calculator

Design PEX layouts for rooms, slabs, snowmelt, geothermal slinkies, zones easily anywhere. Switch between area based and helix modes with engineering safeguards, built-in checks. Set spacing, coverage, tails, waste, and maximum loop limits by diameter. See required length, suggested circuits, per circuit runs, and coil options. Export results to CSV or PDF with click.

Input Configuration White theme
Pick Radiant to size floor loops by area and spacing, or Helix to compute a wound coil length from diameter and pitch.
Radiant / Area-based inputs
%
×
Accounts for serpentine ends, perimeter jogs; typical 1.03–1.10.
%
Typical practice; verify with manufacturer guidance for your product line.
Helix / Spiral inputs
%
Helix length per turn = √[(π·D)2 + p2] where D is mean coil diameter and p is pitch.
Hydraulics Check (optional)
Estimate friction head at your target flow. IDs prefill by chosen size and are editable.
GPM
cSt
~1.0 cSt for water at 20 °C; glycol mixes vary.
in
ft
Smooth PEX ~5×10⁻⁶ ft (≈1.5×10⁻⁶ m).
Results
All values auto-update after clicking Calculate. Unit labels reflect your selection.
Metric Value Units
Total required length–ft
Recommended circuits–loops
Length per circuit (avg)–ft
Max loop guideline–ft
Suggested coil purchase–ft
Suggested manifold size–ports
Hydraulics — Head-Loss Check
MetricValueUnits
Velocity–ft/s
Reynolds number––
Friction factor (Darcy)––
Head per circuit–ft
Head per 100 length–ft/100ft
For parallel circuits on a manifold, pump sees the single-loop head at the governing flow.
Room Grid Visualizer (schematic)
Schematic only. Serpentine path approximates spacing; edges and obstacles not modeled.
Example Data
ModeAreaSpacingCoverageTailsPEXLayoutWasteTurnsPitchDmean
Radiant250 ft²9 in90%30 ft1/2″1.055%———
Radiant120 m²200 mm95%18 m16 mm1.086%———
Helix———20 ft1/2″—3%201.5 in24 in
Formulae Used
  • Radiant / Area-based: Required tube length ≈ L = (A · C) / s · f + T, then apply waste: Lfinal = L · (1 + w).
    Where A is covered area, C coverage fraction, s spacing (same length units as area side), f layout factor (serpentine/perimeter allowance), T tails to manifold, w scrap fraction.
  • Circuit count: N = ceil(Lfinal / Lmax) based on selected PEX size guideline. Average per-circuit ≈ Lfinal/N.
  • Helix / Spiral: Per-turn helix length ℓ = √[(π·D)2 + p2]. Total coil L = N · ℓ + T; then apply waste factor.
  • Head loss (Darcy–Weisbach): hf = f (L/D) (v²/2g) with laminar f=64/Re, or turbulent via Swamee–Jain approximation.
  • Coil purchase suggestion: Greedy fit from common sizes to cover L with minimal overage.
These are planning heuristics; for critical systems verify with detailed hydronic or manufacturer-specific design guidance.
How to Use
  1. Select a mode: Radiant for floors, Helix for wound coils.
  2. Pick units and enter inputs. Watch unit badges update.
  3. For Radiant: set area, spacing, coverage, tails, layout factor, and PEX size.
  4. For Helix: set turns, pitch, mean diameter, tails, and waste.
  5. Optional: fill Hydraulics to estimate head at your target flow.
  6. Click Calculate. Review length, circuits, manifold ports, coil purchase.
  7. Render a schematic grid to visualize spacing; export results to CSV/PDF.
FAQs

Common spacings range 6–12 in (150–300 mm). Tighter spacing improves uniformity but increases length and head loss. Many designs use 8–10 in in living areas and wider in low-load rooms.

They reflect typical hydronic practice balancing flow, temperature drop, and pump sizing: ~200 ft for 3/8″, ~300 ft for 1/2″, ~400 ft for 5/8″, and ~500 ft for 3/4″. Always consult manufacturer specs.

Yes. Use the Coverage input to limit active tubing to the desired percentage of the area, excluding cabinets, hearths, or low-priority zones.

It accounts for extra length not captured by simple area/spacing division—serpentine turnbacks, perimeter jogs, and manifold approach geometry. Values typically range from 1.03 to 1.10.

It’s the average of inner and outer coil diameters: Dmean = (Dinner + Douter)/2. If you only know one diameter, estimate the other using twice the coil thickness.

Pump selection and manifold port/valve authority require hydraulics beyond this scope; this tool provides preliminary head-loss estimation and a simple manifold port suggestion.

Common availability is assumed: 100, 200, 250, 300, 500 ft in US units; 30, 60, 100, 120, 150 m for SI. Adjust purchase to local stock.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.