Trussly code references feature: calculators reference the 2021 IRC (including its NEC-based electrical chapters), the 2021 IPC, and the 2021 IFGC: wire ampacity, stair dimensions, header and joist span tables, drain sizing and slope, and gas pipe sizing. The code section is shown alongside each calculation result. Part of Trussly, a $29.99 iOS app by Creayo LLC.

The code section, not just the answer

Trussly doesn't just give you a wire size. It tells you which ampacity column it used (60°C for NM cable, 75°C only when every termination is rated for it) and where that rule comes from. You get the answer and the code reference so you can verify it yourself or show it to the inspector standing behind you.

NEC for electrical

Wire sizing pulls from NEC 310.16 ampacity tables. Conduit fill calculations reference NEC 314.16 for box fill and Chapter 9 tables for conduit. Voltage drop uses the 3% branch-circuit target from the NEC's informational notes, which is a recommendation, not a requirement. The specific table and section are shown next to every electrical result.

When you're pulling wire for a 60-amp sub-panel 150 feet from the main, you want to know the code backs up the gauge you're buying.

IRC for residential building

Stair calculations reference IRC R311.7 for riser height, tread depth, headroom, and handrail requirements. Floor and deck spans come from IRC Chapter 5 tables, ceiling joists from Chapter 8, and headers from IRC Tables R602.7(1) and (2). The code section sits right next to the calculated value.

Useful when a homeowner asks why the stairs have to be a certain dimension. Point to the code.

IPC and IFGC for plumbing and gas

Drain slope follows IRC P3005.3. Fixture unit counts follow IPC Chapter 7 DFU tables. Gas pipe sizing uses IFGC Tables 402.4(2) and 402.4(28), by Btu/h load and the longest run.

These aren't summaries of the code. They're direct references to the specific table or section that produces the number on your screen.

Reference, not certification

Trussly is a calculator, not a code compliance tool. The references help you look up the right section and understand where the math comes from. Local amendments, inspector interpretations, and job-specific conditions are still on you. Always check with your local authority having jurisdiction. The code references give you a starting point and a citation to work from.

Related features

  • Show Formula -- see the exact equation behind every calculation.
  • PDF Export -- inputs and results in a printable worksheet.

Read more: How to Size Wire for a Circuit (NEC 310.16) | How to Size a Header (IRC R602.7) | Drain Pipe Sizing (IPC DFU Table)

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