App Store/ 2026

FILL

NEC 2023 conduit fill, calculated in seconds.

[ THE PROBLEM ]

I come from a family of electricians. My stepdad was a lifelong IBEW Local 8 electrician in the Toledo area, I worked a summer on one of his crews, and I have cousins and friends in the same union today.

One of those friends texted me: every time he works with an apprentice, they struggle with the same thing: how much wire can legally go in a conduit. He screenshotted the NEC tables and sent them over. That text was the entire product spec.

[ ABOUT ]

FILL takes the guesswork out of conduit sizing for electricians. Pick your raceway type and trade size, add your wire conductors by gauge, and get an instant fill percentage based on NEC 2023 Chapter 9 tables.

Forward and reverse calculations for EMT, RMC, PVC-40, PVC-80, IMC, FMC, LFNC, and more, covering THHN, XHHW, and all standard conductor types. The core calculator is free; FILL Pro is a one-time purchase for extra features. No subscriptions.

[ SCREENS ]

FILL calculator showing 10.4 percent fill for one-inch EMT — The calculator

FILL add wire screen with conductor types and gauges — Adding wires

FILL saved calculation history — History

[ HOW IT WORKS ]

Pick your conduit

Choose from EMT, RMC, PVC-40, PVC-80, IMC, FMC, LFNC, and more. Select your trade size.

Add your wires

Add conductors by wire type and AWG gauge: THHN, XHHW, and more. FILL calculates the fill area in real time as you build your pull.

Check your fill

See your conduit fill percentage instantly with NEC-compliant limits for single, two, and three-or-more conductor runs. Copy or share results right from the app.

[ KEY DECISIONS ]

Let a working electrician be the QA team

I sent every build to my buddy on the jobsite and got back a yes or a 'no, here's what's wrong.' He caught the things I never could have: which raceway types matter, what apprentices actually mix up, how the tables get read in the field. Built in about three days because the feedback loop was that tight.

Design for a gloved hand in the sun

The UI is deliberately brutalist: big buttons, big text, high contrast. An electrician uses this one-handed, outside, with sun glare on the screen, mid-pull. Every layout choice came from that scenario, not from what looks nice in a screenshot.

[ RESULTS ]

190 new userssince launching at the beginning of March.

60 monthly activesin the last 28 days: working electricians who keep coming back to it on the job.

$76 lifetime revenueso far. FILL was built to be useful first; the buy-once Pro tier covers the cost of existing.

[ ON THE JOB ]

FILL in use on a jobsite, held one-handed by an electrician with wire spools and a tool bag in the background — One hand, work gloves, sun glare. The environment the UI was designed for.

[ GET IT ]

FILL is free to download on the App Store. The core calculator costs nothing; FILL Pro is a one-time purchase for extra features.

Download on the App Store