FIG. 01 — TOOL
CONDUIT FILL
CALCULATOR
NEC 2023 compliant. Pick conduit type, add conductors, get the fill percentage with jam-probability analysis. All math runs in your browser — see the underlying wire fill chart for static lookups.
DWGWFC-CALC-001
SH01 / 01
SCALE1 : 1
REFNEC 2023 § CH.9
REVA
FIG. 01 — CONDUIT FILL CALCULATOR
INPUT ▸ CALCULATE ▸ READ
A · CONDUIT TYPE
B · TRADE SIZE
DESCRIPTION
EMT — Electrical Metallic Tubing
C · CONDUCTORS
01
RESULT · FILL %
◆ WITHIN NEC LIMIT
7.5%
OF 40%
ALLOWED
025↑4075100
- CONDUCTORS
- 3
- WIRE AREA
- 0.040in²
- CONDUIT AREA
- 0.533in²
- JAM RISK
- LOW
- Three or more conductors — NEC allows 40% fill.
CONDUIT
EMT · 3/4"
CONDUCTOR
12 AWG · THHN
FIG. 02
HOW TO USE THE CALCULATOR
- 01PICK THE CONDUIT TYPE
EMT, IMC, RMC, PVC Sch 40, PVC Sch 80, FMC, LFNC-B, or ENT. Each has its own NEC Chapter 9 Table 4 interior area.
- 02CHOOSE THE TRADE SIZE
The dropdown only shows sizes valid for the conduit type (LFNC only goes to 2"; RMC and PVC go to 6").
- 03ADD CONDUCTOR ROWS
Each row is one insulation + one gauge + a count. Use the stepper to bump the count quickly.
- 04READ THE RESULT
The instrument panel shows fill %, NEC status, jam probability, and a recommended next-size-up conduit when over fill.
FIG. NEC
NEC CODE REFERENCES
- NEC 2023 CH.9 TABLE 1Percent of cross-section of conduit and tubing for conductors (53/31/40).
- NEC 2023 CH.9 TABLE 4Dimensions and percent area of conduit and tubing.
- NEC 2023 CH.9 TABLE 5Dimensions of insulated conductors.
- NEC 2023, 310.15(C)(1)Adjustment factors for more than three current-carrying conductors (ampacity, separate from fill).
FIG. 03
CONDUIT FILL CALCULATOR · FAQ
Yes. Conductor areas come from NEC Chapter 9 Table 5 and conduit interior areas from Table 4. Fill percentages follow Table 1: 53% (1 conductor), 31% (2 conductors), 40% (3 or more). The calculator's only deviation from printed Annex C tables is the conservative direction — when math gives 21.98 we report 21, not 22.