Conduit Fill
Check what fraction of a conduit the wires occupy.
About Conduit Fill
Total conductor area is divided by the conduit's interior cross-section to get the fill percentage, compared against the common forty percent limit. Overfilling a conduit makes pulling and cooling the conductors difficult, so fill is regulated in the electrical code.
Formula
Conduit Fill
Fill % = (conductors x per-conductor area) / conduit area x 100
- conduit area
- Inside cross-section of the conduit
Worked example
With the default values below, Conduit Fill returns Fill Percentage of 14.2%. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Conductorsminimum 1
- 4
- Area per conductorminimum 0 sq in
- 0.0157 sq in
- Conduit diameterminimum 0.1 in
- 0.75 in
Results
- Conduit Area
- 0.4418 sq in
- Total Conductor Area
- 0.0628 sq in
- Fill Percentage
- 14.2%
- Fill Check
- Within the 40% limit
Step by step
- 1Values used
- 2Conduit Fill
- 3Fill Percentage= 14.2
- 4Conduit Area= 0.4418 sq in
- 5Total Conductor Area= 0.0628 sq in
- 6Fill Check= Within the 40% limit
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Conduit Fill calculated?
Fill % = (conductors x per-conductor area) / conduit area x 100 Total conductor area is divided by the conduit's interior cross-section to get the fill percentage, compared against the common forty percent limit.
Why does Conduit Fill matter?
Overfilling a conduit makes pulling and cooling the conductors difficult, so fill is regulated in the electrical code.
What values do I need to enter?
This calculator takes 3 inputs: Conductors, Area per conductor, Conduit diameter. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.