Electrical Conduit Fill Calculator
Conduit fill percentage from conduit and cable sizes.
Runs in your browser. Nothing is uploaded — your input is processed on this device and discarded when you close the tab.
Electrical Conduit Fill Calculator
How to use this tool
- Enter the conduit internal diameter and the cable outer diameter in millimetres.
- Enter how many identical cables run in the conduit.
- Press Generate to see the fill percentage against the 40% guide limit.
Worked example
A 20 mm internal conduit has area 314.16 sq mm. Four 6 mm cables total 113.10 sq mm, giving 36.00% fill, which passes the 40% guide.
What this tool does not do / Limits
This is a sizing estimate from user-entered values with stated assumptions only, assuming identical round cables. It is explicitly not a substitute for a qualified electrician or local electrical code compliance. Real fill rules vary by cable count, cable type and local code, and pulling ease and bends matter too.
Frequently asked questions
Why is 40% used as the guide?
It is a common fill limit for more than two conductors in many codes, but the applicable limit for your job comes from your local code, not from this tool.
What if my cables differ in size?
This tool assumes identical cables; for mixed sizes, add each cable's area separately and divide by the conduit area.
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