Technical utilities
Conduit Fill Geometry Calculator
Geometric fill equals total conductor circle area divided by raceway circle area. Both areas come directly from the entered outside and inside diameters.
Calculate geometric occupied area and fill percentage from user-entered raceway and conductor diameters.
Calculated result
Geometric fill result
Calculating…
Calculated locally in your browser
Planning math only. Verify equipment specifications and installation requirements separately.
What this calculator returns
The target is yours. Power Totals does not prefill or label a code-permitted percentage.
Formula and variables
The calculation runs entirely in your browser. Static formulas, definitions, examples, and tables remain readable without JavaScript.
Fill% = 100 × quantity × π(OD/2)² / [π(ID/2)²].
- Vdrop
- Voltage lost across the conductor path, in volts.
- I
- Current through the conductor, in amperes.
- R
- Electrical resistance of the modeled conductor path, in ohms.
- ρ
- Material resistivity at the modeled temperature, in ohm-metres.
- L
- Conductor length used by the selected path model.
- A
- Metal cross-sectional area of the conductor.
OD is user-entered conductor outside diameter and ID is user-entered raceway inside diameter.
Worked example
| Input | Value |
|---|---|
| Raceway inner diameter | 25 mm |
| Conductor outer diameter | 6 mm |
| Conductor quantity | 3 |
| Your target fill | 40 % |
Three 6 mm OD conductors in a 25 mm ID raceway occupy about 17.28% of the geometric cross-sectional area.
Reference table
| Example item | Diameter | Circle area |
|---|---|---|
| Conductor A | 4 mm | 12.57 mm² |
| Conductor B | 6 mm | 28.27 mm² |
| Raceway A | 20 mm | 314.16 mm² |
| Raceway B | 25 mm | 490.87 mm² |
| Raceway C | 32 mm | 804.25 mm² |
Frequently asked questions
What does the conduit fill percentage represent?
It is the sum of entered cable-circle areas divided by the entered conduit internal-circle area.
Does circle area prove an installation is permitted?
No. The result is geometry only and does not reproduce code tables, cable definitions, or installation requirements.
Assumptions and limitations
- Pure cross-sectional geometry only.
- No NEC/CEC fill table, cable jamming, bending, installation, or compliance analysis.
Method and sources
Review the electrical formulas, calculation methodology, and reference tables for the references most relevant to this calculation. The broader technical sources index records source scope and verification. Last reviewed .