How many 12 AWG wires fit a 200 mL box?

Table 22 allows 28.7 mL for each 12 AWG conductor, so six fit a 200 mL box with nothing else inside. Add a receptacle, which counts as two allowances, and four is the real limit.

Do bonding conductors count in Canadian box fill?

Bare bonding conductors are not counted at all. The NEC counts all its grounds together as one allowance, and importing that rule into a Canadian calculation makes the box look fuller than the code says it is.

Yes. Rule 12-3034 counts wire connectors at one allowance per pair, sized by the largest conductor entering the box, so six marrettes cost three allowances. The NEC has no equivalent charge, so an American calculation misses it and makes the box look roomier than the CEC actually allows.

Where do I find my box volume?

Canadian boxes are marked with their volume in millilitres, usually stamped or moulded inside the back or printed on the label. That marked figure is the number to use, and it is why this page has no table of standard box sizes.

Box Fill Chart Canada: CEC Table 22

Looking for the American box fill chart? NEC Table 314.16 is here.

Last updated: September 25, 2026

How many wires fit in a box in Canada

CEC Table 22 sets a volume allowance per conductor in millilitres. Unlike the NEC there is no table of standard boxes to look up, because Canadian boxes are marked with their own volume. Read the millilitres off the box, then use the second chart below.

Volume allowance per conductor, CEC Table 22

Wire size	mL
14 AWG	24.6
12 AWG	28.7
10 AWG	36.9
8 AWG	45.1
6 AWG	73.7

Conductors that fit the volume marked on the box

Wire size	100 mL	150 mL	200 mL	250 mL	300 mL	350 mL	400 mL	500 mL
14 AWG	4	6	8	10	12	14	16	20
12 AWG	3	5	6	8	10	12	13	17
10 AWG	2	4	5	6	8	9	10	13
8 AWG	2	3	4	5	6	7	8	11
6 AWG	1	2	2	3	4	4	5	6

Table 22 is reproduced from the rule text as published in Alberta STANDATA 21-ECI-012, cross-checked against a Thomas and Betts Iberville catalogue. The counts are the marked volume divided by that allowance, then truncated. The volumes across the top are common marked sizes offered as a lookup, not code values, because no table of standard Canadian boxes exists to publish. How we verify.

What else takes up room, and what does not

Bare bonding conductors are NEVER counted. This is the difference most often got wrong online, because calculators written for the NEC import its all-grounds allowance into Canadian mode, where it does not belong.

Wire connectors, marrettes, DO count in Canada, at one allowance per PAIR, sized by the largest conductor entering the box. The NEC counts them as nothing.

Internal cable clamps get no allowance at all under Rule 12-3034(5). A device on a strap still counts as two allowances. A device measuring more than 2.54 cm from its mounting strap to its back also takes space off the box: 32 cm³ for every centimetre of the device's FULL depth, not just the part beyond 2.54 cm, so a 4 cm device costs 128 cm³.

So the chart is a ceiling for an empty box. Take off the marrette pairs and the devices before deciding a box is big enough, or let the calculator do it with your real contents: Box Fill calculator

The United States does this differently

The NEC works in cubic inches and its allowances run about one step larger: 14 AWG is 2.0 cu in, near 32.8 mL, against 24.6 mL here. It also counts all grounds together as one allowance, charges an internal clamp one allowance and counts wire connectors as nothing. An American box fill number is not a Canadian one.

Box Fill calculator · Conduit fill chart · Wire ampacity chart

Common questions

How many 12 AWG wires fit a 200 mL box?: Table 22 allows 28.7 mL for each 12 AWG conductor, so six fit a 200 mL box with nothing else inside. Add a receptacle, which counts as two allowances, and four is the real limit.
Do bonding conductors count in Canadian box fill?: Bare bonding conductors are not counted at all. The NEC counts all its grounds together as one allowance, and importing that rule into a Canadian calculation makes the box look fuller than the code says it is.
Do marrettes count?: Yes. Rule 12-3034 counts wire connectors at one allowance per pair, sized by the largest conductor entering the box, so six marrettes cost three allowances. The NEC has no equivalent charge, so an American calculation misses it and makes the box look roomier than the CEC actually allows.
Where do I find my box volume?: Canadian boxes are marked with their volume in millilitres, usually stamped or moulded inside the back or printed on the label. That marked figure is the number to use, and it is why this page has no table of standard box sizes.