ElectraKit
Raceways and boxes

Conduit Fill Calculator

Estimate raceway fill from the raceway inside diameter and the quantity and outside diameter of each conductor group.

Raceway inputs

Raceway and conductors

in

Use the manufacturer's listed inside diameter, not trade size.

wires
in
Estimated raceway fill
6.6% filled
Applicable fill limit40%
Available area to limit0.178 in²

Entered conductors are within the selected fill limit. Raceway area: 0.533 in².

Reference onlyThis estimate applies the general 53%, 31%, or 40% fill limits based on conductor count. It does not check conductor ampacity, insulation dimensions, nipple allowances, or other installation-specific requirements. Verify the adopted code and product data.

About this calculator

This calculator adds the cross-sectional area of the entered conductors and compares it with the raceway’s internal area. It supports multiple conductor groups with different outside diameters.

Use listed product dimensions for both the raceway and conductors. This estimate does not determine whether a raceway or conductor is suitable for a particular installation.

Method and assumptions

Conductor area is calculated as the sum of each group’s quantity multiplied by the area of one conductor. Raceway area is calculated from the entered inside diameter. Fill percentage is conductor area divided by raceway area.

The general fill limits used here are 53% for one conductor, 31% for two conductors, and 40% for more than two. Special cases, including short nipples, are outside this estimate.

FAQs

Should I enter trade size or inside diameter?

Enter the raceway inside diameter in inches. Trade size is a nominal designation and may not equal the actual inside diameter. Use product data for the raceway being installed.

How do I find conductor outside diameter?

Use the conductor manufacturer’s product data for the exact conductor type and insulation. Nominal AWG size alone does not provide the outside diameter needed for this estimate.

Does this confirm the raceway installation meets code?

No. This tool compares entered conductor area with the general fill percentages. It does not evaluate every code exception, conductor ampacity adjustment, installation condition, or local amendment.

Related tools

Raceway Fill and Ampacity CalculatorCheck mixed conductor fill and ampacity adjustments together.Voltage Drop and Wire Size CalculatorEstimate circuit voltage loss and compare conductor sizes.Conductor Ampacity CalculatorApply conductor temperature and current-count corrections.

Sources

  • NEC Chapter 9, Table 1: general raceway fill percentages. Verify the adopted edition and local amendments.
  • Raceway and conductor inside/outside dimensions: manufacturer product data for the exact listed products.