Conduit fill
17.1%of conduit area
Within allowed limit
40% allowed · NEC Ch. 9, Table 1
FREE NEC 2023 CALCULATOR
Conduit fill & ampacity derating calculator.
Check wire fill, conductor derating and termination limits together. Know before you pull.
NEC 2023 Code-backed results Free to use Built for electricians
YOUR PULL, CHECKEDSAMPLE
YOUR PULL, CHECKED.EXAMPLE PULL
PASS
This pull meets the checked fill and ampacity limits.
Real ampacity
32 Aallowable after derating
Covers your 30 A load
310.15(C)(1) + Table 310.16
Within the checked limits.
Fill, derating, and terminations work together here. Ordinary small-wire protection: 30 A max.
A field check, not an inspection guarantee. Verify the adopted NEC edition, equipment listings, breaker selection, and local requirements with your AHJ.
Show the calculation
Fill: 0.1477 in² ÷ 0.864 in² = 17.09%. Allowed area: 0.346 in². Verdict uses unrounded areas.
#10 AWG: 40 A × 80% conductor adjustment × 100% ambient correction = 32 A. Capped at 35 A for 75°C terminations → 32 A.
Required: 30 A × 100% noncontinuous = 30 A. Every circuit group is checked against this load.
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BEFORE THE WIRE GOES IN
Conduit fill and ampacity derating calculator
PassPull checks how much space your conductors occupy, how conductor count and ambient temperature affect ampacity, and where equipment termination ratings limit the result. Use one NEC 2023 setup for all three checks.
Choose EMT, PVC Schedule 40, RMC or IMC; enter every conductor, the current-carrying count, termination rating and required load; then check the result. See the supported sizes and assumptions before relying on a setup.
Conduit fill vs. ampacity derating: check both
Space in the pipe and allowable current are different limits. Check both before deciding that a pull works.
Read the guideHow to count current-carrying conductors
The number used for heat adjustment is often different from the number used for physical fill.
Read the guide60°C, 75°C and 90°C termination ratings explained
The wire jacket and the equipment connections place different limits on a circuit.
Read the guideHow many 12 AWG THHN wires fit in EMT?
For physical fill, ½-inch EMT takes 9, ¾-inch takes 16, and 1-inch takes 26 same-size 12 AWG THHN/THWN-2 wires. Ampacity derating is a separate check.
Read the guideDoes PassPull calculate cable pulling tension?
PassPull checks conduit fill and electrical ampacity limits. It does not calculate pulling tension, sidewall pressure, jam ratio or the force needed to pull cable. See the full calculation scope.
How many 12 AWG THHN wires fit in EMT?
For physical fill with every wire the same size and insulation, ½-inch EMT takes 9, ¾-inch takes 16, and 1-inch takes 26. Grounds take up space too; the allowable current needs a separate check. See the wire-count chart and worked derating examples.
Does PASS mean my installation will pass inspection?
It means your inputs meet the implemented checks within the supported scope. It does not evaluate the entire installation or replace your adopted NEC, equipment listings, and local inspector’s requirements.
Will a larger pipe fix an ampacity failure?
It can reduce the fill percentage. The same current-carrying count still receives the same adjustment factor. Try a suitable larger circuit conductor, or plan separate raceways for complete circuits and recheck each one.
Do I need an account to save or share?
No. Save up to 20 named pulls in this browser, copy a setup link, or download a field-check record. Local saves do not sync between devices. A shared setup must be checked again by its recipient.