How to Use the Conduit Fill Calculator
Step-by-Step Guide
1
Select Conduit Type
Choose your conduit type from the dropdown menu: EMT, PVC (Schedule 40 or 80), RMC, IMC, or FMC. Each type has different inner diameter specifications.
2
Choose Conduit Size
Select the trade size of your conduit, ranging from 1/2" to 6". The calculator uses the actual inner diameter for accurate calculations.
3
Select Installation Type
Choose between "Standard Installation" or "Nipple" (for conduits 24" or less). Nipples allow 60% fill instead of the standard percentages.
4
Add Conductors
For each conductor type:
- Select wire type (THHN/THWN, XHHW, THW)
- Choose wire size (14 AWG to 750 kcmil)
- Enter the quantity of conductors
- Click "Add Conductor" to include multiple wire types/sizes
5
Calculate Results
Click "Calculate Conduit Fill" to see your results. The calculator will show fill percentage, pass/fail status, and a visual diagram.
Understanding NEC Fill Requirements
| Number of Conductors | Maximum Fill % | Application |
|---|---|---|
| 1 | 53% | Single conductor installations |
| 2 | 31% | Two conductor installations |
| 3 or more | 40% | Standard multi-conductor runs |
| Any (Nipple) | 60% | Conduits 24" or less in length |
Common Terms
- Conduit Fill
- The percentage of the conduit's cross-sectional area occupied by conductors.
- Trade Size
- The nominal size designation for conduits (e.g., 1/2", 3/4", 1").
- AWG
- American Wire Gauge - standard for wire diameter sizing.
- kcmil
- Thousand circular mils - unit for large conductor sizes.
- Nipple
- A short conduit section (24 inches or less) connecting two enclosures.
Pro Tips
- Always verify calculations with local codes and amendments
- Consider derating factors for ambient temperature and bundling
- Leave room for future conductor additions when possible
- Use the export feature to document your calculations