Raceway planning tool

Conduit Fill Calculator and Wire Fill Chart

Check the occupied area of a conductor or cable bundle, compare available raceway sizes, and see which fill rule applies. Use a named manufacturer preset or enter the exact dimensions for the products in your installation.

Sources, dimensions, and calculation rules reviewed August 21, 2026

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Enter the exact raceway and items

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1. Raceway

Manufacturer product or custom inputPresets use the named manufacturer's published nominal inside diameter.

Trade sizeTrade size is a product label; the calculation uses the displayed inside diameter.

Scope: the Chapter 9 percentage table is for complete conduit or tubing systems, not isolated sections used only to protect exposed wiring or cable from physical damage.

Use the qualifying short-raceway nipple 60% limit

Select only for a raceway nipple no longer than 600 mm (24 in.) between enclosures. Under the publisher-current wording, connector lengths are excluded from that 24-inch measurement. Verify every other condition, the adopted edition, and local amendments with the AHJ.

2. Conductors and cables

Each row can use a Southwire product-specific finished diameter or your own conductor/cable dimension. Include equipment grounding and bonding conductors.

Product and conductor sizeApproximate finished outside diameter: 0.122 in; solid copper.

QuantityPositive whole number

At least one valid item and a strict positive whole-number quantity are required.

Within selected fill limit

Wheatland steel EMT, trade size 3/4" · 40% selected limit

Occupied area: 8.77%Selected limit: 40%

Total items: 4
Occupied area: 0.04676 in²
Raceway area: 0.5333 in²
Nominal limit area: 0.2133 in²

Nominal area headroom is 0.1665 in². This is not permission to add another conductor or cable: changing the item count can change the applicable fill limit.

Selected product family

Minimum-size comparison for Wheatland steel EMT

First listed size within the selected limit: 1/2"

This comparison changes only the trade size within the named manufacturer product. It is not a generic maximum-wire-count table.

Wheatland steel EMT trade-size results for 4 total items
Trade size	Inside diameter	Internal area	Fill used	Selected limit	Result
1/2"Minimum	0.622 in	0.3039 in²	15.4%	40%	Within
3/4"Selected	0.824 in	0.5333 in²	8.77%	40%	Within
1"	1.049 in	0.8643 in²	5.41%	40%	Within
1-1/4"	1.380 in	1.496 in²	3.13%	40%	Within
1-1/2"	1.610 in	2.036 in²	2.30%	40%	Within
2"	2.067 in	3.356 in²	1.39%	40%	Within
2-1/2"	2.731 in	5.858 in²	0.80%	40%	Within
3"	3.356 in	8.846 in²	0.53%	40%	Within
3-1/2"	3.834 in	11.545 in²	0.41%	40%	Within
4"	4.334 in	14.753 in²	0.32%	40%	Within

NEC / NFPA 70 raceway fill limits at a glance

NFPA 70®, National Electrical Code® (NEC®), Chapter 9 uses 53% for one conductor or cable, 31% for two, and 40% for more than two. A separate 60% allowance can apply to a qualifying raceway nipple no longer than 24 inches between enclosures.

Raceway fill percentage chart
Raceway contents	Maximum occupied area	When to use it
1 conductor or cable	53%	One item occupies the raceway
2 conductors or cables	31%	Two total items occupy the raceway
More than 2	40%	Three or more total items occupy the raceway
Qualifying raceway nipple	60%	No longer than 600 mm (24 in.) between enclosures; verify all adopted-code conditions

These percentages are the publisher-current NFPA 70, Chapter 9 fill rules. The current publisher edition is 2026, but jurisdictions may enforce 2023, 2020, an older edition, or local amendments. Confirm the adopted rule with the authority having jurisdiction (AHJ).

Chapter 9 Note (2) limits this percentage table to complete conduit or tubing systems. It is not intended for isolated conduit or tubing sections used only to protect exposed wiring or cable from physical damage.

How this conduit fill calculator works

Measure the raceway

Internal area is calculated from the selected product's nominal inside diameter or your custom value.

Add occupied area

Each conductor or cable's circular area is multiplied by its strict whole-number quantity and summed.

Apply the right limit

The tool selects 53%, 31%, or 40% by total item count, or 60% only when you explicitly select the nipple mode.

Area of a round item = π × diameter² ÷ 4

Occupied area = Σ(quantity × item area)

Fill percentage = occupied area ÷ raceway internal area × 100

The minimum-size comparison repeats the same calculation across the selected manufacturer's available trade sizes. It does not substitute a different raceway product silently. If your exact product differs, use its datasheet dimensions in custom mode.

The 0.8 maximum-count rule is narrow

For a maximum-count calculation containing conductors or cables of the same size, a quotient with a fractional part of 0.8 or more may use the next whole number. A separate sentence in Note (7) permits one conductor or cable in a single-item sizing calculation when the quotient is at least 0.8. These exceptions can make a result acceptable even when a raw area comparison is above the nominal percentage limit.

The calculator never applies that rounding to mixed bundles. Different sizes, insulation constructions, custom cable entries, or product variants are compared by their combined area without a count round-up. When the rule changes a result, the result card names it explicitly.

What dimensions should you enter?

Raceway

Use the exact product's published internal diameter or internal area. Trade size is a name, not the actual inside diameter. Presets on this page are tied to Wheatland steel raceway or JM Eagle PVC product data.

Conductors and cables

Use the finished outside diameter, including insulation and jacket. Presets are specific Southwire SIMpull copper constructions. A multiconductor cable counts as one item; for an elliptical cable, enter its major diameter.

Include every equipment grounding and bonding conductor using its installed insulated or bare dimension.
Do not use bare copper diameter for an insulated conductor; the insulation occupies raceway area.
PVC presets stop at trade size 6. Larger PVC conduit is subject to edition-specific listing and installation conditions that this fill-area tool does not evaluate.
Manufacturer dimensions can be nominal or approximate and have tolerances. Verify the current datasheet and exact stock construction.

A fill-area result is not full electrical-code compliance

This tool checks cross-sectional raceway fill only. It does not check ampacity adjustment or derating, conductor ampacity or insulation suitability, grounding and bonding design, pulling tension, clearance, full jamming risk, bend limits, box or pull-box sizing, environmental listing, or local amendments. The limited three-identical-item ratio warning is only a screening flag.

Verify the product dimensions, the NFPA 70 edition and amendments adopted where the work is located, and the complete installation with the AHJ or a qualified electrical professional. CalculatorFlux is not affiliated with or endorsed by NFPA.

Conduit fill calculator FAQs

What are the 53%, 31%, and 40% raceway fill limits?

The Chapter 9 fill limits are 53% of the raceway's internal area for one conductor or cable, 31% for two, and 40% for more than two. The applicable limit is based on the total number of conductors and cables occupying the raceway, not the number of circuits.

When can a raceway nipple use the 60% fill allowance?

A 60% allowance may apply to a qualifying raceway nipple no longer than 600 mm (24 in.) between enclosures. Under the publisher-current wording, connector lengths are excluded from that measurement. Select this mode only when the entire section meets the conditions in the edition adopted by the authority having jurisdiction.

Does the equipment grounding conductor count for conduit fill?

Yes. Equipment grounding and bonding conductors occupy space and must be included. Use the actual dimension for the installed insulated or bare conductor. This tool does not determine whether a grounding or bonding conductor is correctly sized.

Can I enter a multiconductor or elliptical cable?

Yes. Add each multiconductor cable as one item and enter its actual overall diameter. For an elliptical cable, use the major diameter as though it were a round cable. Confirm the dimension on the exact manufacturer's datasheet.

Why can identical conductors sometimes round up?

When a maximum-count calculation is for conductors or cables of the same size and the quotient's fractional part is 0.8 or more, the next whole number may be permitted. The rule also permits one item in a single-item sizing calculation when the quotient is at least 0.8. It is not applied to mixed-size bundles, and this calculator shows when it changes a result.

Are the manufacturer presets the same as generic NEC table values?

No. Every preset is tied to a named manufacturer's published nominal or approximate dimension. Product dimensions and tolerances can change, so select the exact product when available or enter the current actual dimension from its datasheet. The presets are not a reproduction of the NEC raceway or conductor tables.

Does a result mean the installation is NEC compliant?

No. The result checks occupied cross-sectional area against the selected fill rule only. It does not check ampacity adjustment, conductor suitability, grounding and bonding design, pulling tension, clearance, full jamming risk, bends, box sizing, local amendments, or which NFPA 70 edition the authority having jurisdiction adopted.

Sources and data provenance

The calculator uses a short statement of the fill rules and independently calculates geometry from current manufacturer dimensions. It does not reproduce NFPA's Chapter 9 raceway, conductor, or maximum-count tables.

Method and source review: August 21, 2026. Inputs stay in the browser; this calculator does not send project dimensions to a server.