Four trades. One calculator app. Built for the field.
FieldDojo is the trade calculator app built for the back of the truck — concrete, BTU, wire size, fixture units — with the code reference printed next to every answer. Stop doing trade math on scrap paper.
Trade math on scrap paper costs you money.
The notebook in your truck doesn't cite NEC. The calculator on your phone doesn't know what a board foot is. Spreadsheets don't open in a basement.
15.36 m³??
+ 10% waste = ~17?
order 18 yds
RECONVERT TO YD³
~20-21 yd³ order what?
60 ÷ ?? = ___
8 AWGundersized
10 AWG too small
need NEC chart
no signal · book in van
→ drive back ↩
One thumb. Right answer. Code attached.
Four trades. 57 calculators. Zero generic math.
Tap a trade to see what's inside.
Pour the slab,
not the math.
Concrete, framing, drywall, roofing, stairs, decks, tile, pavers — 26 calculators, every formula a foreman reaches for on one screen.
- ✓Concrete volumeCubic yards or m³ for footings, slabs, walls, columns.
L × W × D - ✓Lumber & board feetBoard feet from dimensions. Stud count for any wall length and OC spacing.
- ✓Drywall, roofing, paintSheets needed, roofing squares, paint coverage by gallon — waste factor included.
Sized right.
First time.
BTU load, duct sizing, refrigerant charge, heat loss, SEER savings — eight calculators built for HVAC technicians. Numbers for the homeowner, not vibes.
- ✓BTU loadHeating & cooling load by climate zone, insulation, square footage.
- ✓Duct sizingRound & rectangular dimensions for target CFM and friction rate.
- ✓Refrigerant & ACHSubcooling and superheat calcs. Air changes per hour for any room.
ASHRAE 62.1
Code-cited
amperage.
Wire size, voltage drop, conduit fill, panel load, motor FLA, transformer kVA — 14 calculators for electricians, every result tagged with its NEC article. Inspector ready.
- ✓Wire gauge & voltage dropSizing for any amperage and run length.
NEC 310.16 - ✓Conduit fillEMT, IMC, RMC, ENT — all wire combinations.
NEC Chapter 9 - ✓Panel loadConnected and demand loads, balanced across phases.
NEC Article 220
Fixture units,
fixed.
Pipe sizing, flow rate, drain slope, gas pipe, septic, water heaters, fixture units — nine calculators for plumbers, no dog-eared table on the truck dash.
- ✓Pipe sizing & flowDiameter, flow, velocity for water supply, drainage, gas piping.
- ✓Fixture unitsWSFU and DFU per IPC and UPC.
UPC Table 6-3 - ✓Slope & water heaterDrain slope, fall-per-foot. WH sizing by occupancy.
A real calculator. Right here.
Pick a job — see FieldDojo solve it with the formula and code reference attached.
Pick a job.
See the math.
This is the same calculator that ships on iOS and Android. Tap a scenario and watch the result animate in.
Designed for gloves, sun, and zero signal.
Every screen assumes you're wearing gloves, standing in the sun, and holding a phone with no bars. Because that's where the work happens.
Every result ships with the
code reference attached.
NEC 310.16 next to every wire size. ASHRAE 62.1 next to every ACH. Hand the inspector your phone, not a wink.
One tap. Inches to mm,
BTU to kW, gallons to litres.
Set it once in Settings. Every calculator, every result switches. No conversion factor on a Post-it.
No signal? No problem.
Every calc runs on-device. Basements, tunnels, rural service — everything works.
Big targets. High contrast.
Outdoor mode.
56pt minimum tap targets — well above Apple's 44pt floor. Auto-bumps contrast in direct sun.
Share any result as text.
PDF export lands with Pro.
Every calculation's history is one tap — send via Messages, email, or AirDrop today. Formatted PDF reports arrive with Pro.
Your data stays on your device.
No account required. No ads. Ever.
Calculations live in local storage, not on our servers. Use it anonymously — or sign in with Apple, Google, or email when you want backup and sync.
Inputs remember
between sessions.
Open the slab calc tomorrow — yesterday's dimensions are still there. Pick up where you left off.
The math, written out.
Every calculator in the app has a method behind it. These walk through the code sections, the formulas, and the worked examples — free to read, no app required.
- What rise and run for these stairs?Stair Rise and Run: Code Limits for the US, Canada, and the UKconstruction
- How big a service does this house need?Residential Electrical Load Calculation: NEC Article 220 Guideelectrical
- How many BTUs does this house need?Manual J Heat Load Calculation: HVAC Sizing Guide for TechniciansHVAC
- How many wires fit in this conduit?Conduit Fill Calculations: NEC Chapter 9 Guide for Electricianselectrical
- What size pipe for this fixture load?Pipe Sizing for Plumbers: Water Supply, Drainage, and Gas Pipingplumbing
- How much concrete do I need?How to Calculate Concrete for Footings, Slabs, and Columnsconstruction
- What size duct for this room?Duct Sizing for HVAC: The ASHRAE Equal Friction Method ExplainedHVAC
- What size wire do I need?Wire Sizing and Voltage Drop: What Every Electrician Needs to Knowelectrical
All 57 calculators stay free. Pro is live now.
Every calculator is free on iOS and Android — nothing to buy, no trial timer. Pro adds cloud sync, PDF export, unlimited history, and unlimited projects for $4.99 a month, $29.99 a year, or $79.99 once.
- All 57 calculators
- NEC, ASHRAE, UPC, IPC & more references
- Imperial ↔ Metric toggle
- Last 30 calculations saved locally
- 1 project to organize a job
- Offline-first, no ads
- Everything in Free
- Unlimited calculation history
- Cloud backup & cross-device sync
- PDF export & share
- Unlimited projects
- Priority support
- MonthlyRolling, cancel anytime$4.99
- YearlySave 50% vs monthly$29.99
- LifetimeOne-time, never renews$79.99
Free on the App Store and Google Play · Pro $4.99/mo, $29.99/yr, or $79.99 lifetime · cancel anytime
Everything you'd ask a buddy.
Get it on the rig.
FieldDojo is out on both stores. All 57 calculators, free — no account, no ads, no trial timer.