WireGaugeCalc Free calculator · NEC cited · works offline
Fill A 5.5 By 2.5 Box
Fill a 5.5 by 2.5 box is quick with WireGaugeCalc, since you enter the conductors, devices, and clamps inside.
The calculator adds the volume each item needs and compares it to the cubic inches the box holds.
So you know if the box has room before you crowd it and fail an inspection.
Open the calculatorEnter any two values and read the rest.
Ohm’s law: V = I × R and P = V × I. Field aid only, verify against the current NEC and your local authority having jurisdiction.
Count Conductor Volume In The Box
NEC 314.16(B) assigns a fixed volume to each conductor by gauge, so the count and size drive the total.
WireGaugeCalc tallies hot, neutral, ground, devices, and clamps, then sums the cubic inches required.
Since the box marking lists its true volume, the tool compares your total to that number.
Check Cubic Inch Capacity Before You Wire
The calculator decides if a 5.5 by 2.5 box has room using these counts:
- Current-carrying conductors by gauge
- Equipment grounding conductors, counted as one
- Devices such as switches and receptacles
- Internal cable clamps in the box
- Total volume against the box cubic inch rating
One app for every NEC calculation
WireGaugeCalc keeps the calculations you reach for most in one place:
- Voltage drop and wire sizing for any run
- Conduit fill for EMT, PVC, and RMC
- Box fill and junction box sizing
- Ampacity and temperature derating
- Motor circuit and load calculations
- Conduit bend offsets and saddles
Built for the field, works offline
The whole app runs on your phone, so it keeps working in a basement, an attic, or a job site with no signal.
There is no account to create and nothing to load. Open it, run the number, and get back to work.
- No signup and no signal needed
- Answers in a tap, not a spreadsheet
- Same tool on phone, tablet, and desktop
Every result cites the NEC article
Each answer shows the table or formula it came from, so you can check the method and learn the code as you go.
That makes the app useful on the job and during exam prep, since the reasoning is right next to the number.
Switch the code year your job runs on
Jurisdictions adopt the NEC at different times, so you can match the calculation to the code in force:
- NEC 2017, 2020, and 2023 tables
- Copper and aluminum conductors
- 60, 75, and 90 degree C terminations
- Single-phase and three-phase systems
Run the number, then get back to work
Stop flipping through a paper book or hopping between calculator sites. Enter your values, read the code-cited answer, and move on. Free to use, no signup.
Open the calculatorFrequently asked questions
How do I find the cubic inch volume of my box?
A listed box is stamped with its volume in cubic inches, usually on the inside back or a wall. Use that marked value, not the rough outside dimensions, when you check box fill.
Does the ground wire count toward box fill?
All equipment grounding conductors together count as one conductor at the largest ground volume per NEC 314.16(B). Verify your fill calculation against the current NEC and your local authority having jurisdiction.
Is WireGaugeCalc free to use?
Yes. Every calculator is free to run with no signup. A paid tier adds saved projects, PDF reports, and extra code years, but the core math stays free.
Does it work without internet?
Yes. The app runs on your device, so it keeps working with no signal on a job site, in a basement, or in an attic.
Are the results code accurate?
Results follow published NEC tables and standard formulas, and each answer shows the article it came from. It is a field aid, not a stamp of approval, so verify against the current code and your local authority before you wire anything.
Which NEC code year does it use?
You can switch between NEC 2017, 2020, and 2023, since jurisdictions adopt the code at different times. Pick the year your job runs on.