CEC Box Fill Calculator
Check whether your device or junction box is big enough under the 2024 Canadian Electrical Code — Rule 12-3034 / 12-3036 and the Table 22 volume allowances. No signup.
Add the conductors that enter and stay in the box. Pigtails that start and end inside the box don't count.
Modern boxes are stamped with their volume. Enter it, or tap a common box above.
Sizing the box is quick. Pricing the whole job isn't.
VoltiQ turns a plain-language job description into a fully itemized estimate — labour, materials, and CEC code flags — in about three minutes. Built in New Brunswick for Atlantic Canada electricians.
Try VoltiQ free — no signupHow box fill works in the Canadian Electrical Code
Box fill is governed by CEC Rule 12-3034 and Rule 12-3036. Every box has a usable volume (stamped on modern boxes, in cm³). You add up a volume allowance for everything inside, and the box must be at least that big.
CEC Table 22 — volume allowance per conductor
| Conductor size | Volume allowance |
|---|---|
| 14 AWG | 24.6 cm³ (1.5 in³) |
| 12 AWG | 28.7 cm³ (1.75 in³) |
| 10 AWG | 36.9 cm³ (2.25 in³) |
| 8 AWG | 45.1 cm³ (2.75 in³) |
| 6 AWG | 73.7 cm³ (4.5 in³) |
Note: these Canadian allowances are smaller than the US NEC values — don't mix the two.
What counts
- Each conductor entering and staying in the box — one allowance for its size
- Each flush device (switch/receptacle strap) — 2 × the largest conductor
- All internal cable clamps together — 1 × the largest conductor
- Each fixture stud or hickey — 1 × the largest conductor
- All bonding (ground) conductors together — 1 × the largest bonding conductor
What doesn't count
- Pigtails and jumpers that both start and end inside the box
- Wire connectors (marrettes) themselves
Frequently asked questions
How do you calculate box fill in Canada?
Add a Table 22 volume allowance for each conductor, add 2× the largest conductor for every device, 1× the largest for all clamps together, 1× for each fixture stud, and 1× for all bonding conductors together. The box's marked volume must be at least that total. This calculator does it for you.
Why are the CEC numbers different from the NEC?
Canada (CEC Table 22) and the US (NEC 314.16) use different volume allowances. A #14 is 24.6 cm³ in Canada versus about 32.8 cm³ (2.0 in³) in the US. Always use the Canadian values here.
Does the ground wire count?
All bonding conductors in the box together count as a single allowance, based on the largest one — not one each.
Is it free?
Completely free, no signup. It's made by VoltiQ, an AI electrical-estimating tool for Atlantic Canada contractors.