Conduit Fill · Free · Same math as the app
Conduit Fill Calculator
Will this many cables fit this raceway? Pick the raceway, trade size and cable, and get the fill against the allowance for that count, the most cables the size carries, and the jam check.
Conduit fill
24.5%of 40% allowed
PASS
Max cables this size4
- Raceway area
- 0.864 in²
- Cable area × 3
- 0.212 in²
- Usable at 40%
- 0.346 in²
- Max cables this size
- 4
NEC Ch. 9 Tbl 1: 1 cable 53%, 2 cables 31%, over 2 cables 40%. Areas from Tbl 4 nominal ID 1.049". Fill is geometry only; it says nothing about pull tension.
Opens this in the VoltIQ app with your numbers. Add your name and the job, then save it or send it to the crew.
No signal needed
This page needs signal. The app doesn't.
In the riser, the basement or above the ceiling, VoltIQ runs this calculation with no bars. Then it puts the answer on a Printout with your name on it.
How it works
The calculator takes the area inside the raceway from the nominal inside diameter for its type and trade size, and the area of one cable from its outside diameter. It multiplies the cable area by the quantity, divides by the raceway area, and checks that percentage against the allowance for the count: 53% for one cable, 31% for two, 40% for three or more.
Picking a listed cable fills in its diameter. Typing or stepping the diameter switches the cable to Custom: the cable's name only labels the result, and the math reads the diameter. The quantity has to be a whole number, 1 or more. Anything else gets a message under the field and no result, since the allowance depends on the count.
It covers EMT, PVC Sch 40, PVC Sch 80, RMC (rigid) and IMC, from 1/2" to 4".
The calculator opens on 3 Cat6A UTP at 0.300" in 1" EMT. The cables take 0.212 in² of the raceway's 0.864 in²: 24.5%, against 40% allowed. That's a PASS, and the same size carries up to 4 of that cable.
Reading the result
The big number is the fill, next to the allowance it's judged against. The stamp beside it is one of three.
- PASS: the fill is at or under the allowance.
- TIGHT: over the allowance by no more than 12% of it. It's still over. 3 RG11 coax in 1" EMT fill 44.7% against 40%: TIGHT.
- OVER: more than 12% past the allowance. 10 Cat6 UTP in 1" EMT fill 50.2%: OVER. That size carries 7 of them.
When the fill is over, the fix line names the smallest trade size of the same raceway that brings it under the allowance. For the RG11 run it reads “Go to 1-1/4" EMT and it lands under 40%.” If no size up to 4" carries the count, it tells you to split the run.
Under that are the working figures: the raceway area, the cable area times the quantity, the usable area at the allowance, and Max cables this size. That last one is the most cables of this diameter the size carries at their allowance. It counts to 400 and stops.
WON'T PASS, WON'T LAST, JUST UGLY
Each concern is filed under one of three tags, with its math underneath.
- WON'T PASS shows whenever the fill is over the allowance, TIGHT or OVER. The math gives the percent used against the percent allowed, and the two areas.
-
WON'T LAST is the jam check. It runs only at exactly three cables, and fires when the conduit's
inside diameter divided by the cable's outside diameter lands from 2.80 to 3.20. In that window three cables of
equal diameter can wedge at a bend: the pull goes fine and the cable is damaged on the way through. It shows even
when the fill passes. 3 Cat6 F/UTP in 3/4" IMC fill
29.3%, a PASS, and the math reads
conduit ID ÷ cable OD = 3.20 (2.80 to 3.20 is the jam band). -
JUST UGLY shows when the run passes but uses more than 85% of its allowance, and there's no jam
warning. The math gives the headroom left. 4 Cat6A S/FTP in
1" EMT fill 34.9%: a PASS with
5.1% headroom remaining.
What it doesn't check
- Pull tension, bends and run length. Fill is geometry only. For the bend itself, use the bend radius calculator.
- Mixed cables. It uses one diameter for every cable in the run.
- Your exact conduit and cable. Raceway areas come from the nominal inside diameter for the type and size. Each listed cable has one diameter; if your spec sheet says different, type the sheet's number.
- Other raceways. Cable tray, innerduct and flexible conduit aren't on the list, and nothing past 4" is.
Questions
How many Cat6 cables fit in 3/4" EMT?
Max cables this size reads 4 at the 0.235" diameter the app lists for Cat6 UTP. In 1" EMT it's 7. Diameters vary by manufacturer: type the one on your cable's spec sheet.
How many Cat6A cables fit in 1" EMT?
Max cables this size reads 4 at the 0.300" diameter the app lists for Cat6A UTP. At 3 cables the fill is 24.5% of 40% allowed. In 3/4" EMT it's 3.
What fill percentage does it use?
It sets the allowance by cable count: 53% of the raceway area for one cable, 31% for two, and 40% for three or more, per NEC Chapter 9, Table 1. Two cables get the lowest allowance of the three.
Is TIGHT a pass?
No. TIGHT means the fill is over the allowance by no more than 12% of it. It carries the same WON'T PASS line and the same fix as OVER. The stamp tells you how far over you are, not whether you're over.
Can I mix cable sizes in one run?
Not in one calculation. It uses one diameter for every cable in the run. Entering the largest cable's diameter for all of them gives a fill at least as high as the real one.