Conduit / Tray Fill
Define the conduit (or tray) and the cables with their outer diameter and I compute the fill percentage, the NEC limit (40% for 3+ cables) and how many more cables fit.
—
How it is computed · NEC Ch.9 Table 1 fill
1. Area of each round cable:
π × (OD/2)², with the OD (outer diameter) in mm.
2. Duct area: round conduit π × (Ø/2)²;
rectangular tray width × height, in mm².
3. Fill:
fill% = Σ(cable area × qty) / duct area × 100.
4. NEC limit by total number of conductors:
1 cable → 53%, 2 cables → 31%,
3 or more → 40%.
5. Extra cables that fit:
floor((duct area × limit − used area) / one-cable area),
using the largest-diameter cable as the reference (conservative).
6. Real fill also depends on the bend radius,
elbows and pull ease. These figures are for sizing,
not a replacement for the manufacturer's table or the local electrical code.
Runs locally in your browser · no sign-up · nothing leaves your browser