Free Tools
Free Tools for Trade Contractors
NEC-compliant electrical calculators and business tools — no login, no email, no ads. Built for electricians, plumbers, and HVAC contractors.
Business Tools
Missed Call Revenue Calculator
See exactly how much revenue your business loses from unanswered calls each month — broken down by day, week, and year.
Service Pricing Calculator
Calculate your true hourly rate based on income goals, overhead, taxes, and billable hours. Includes trade-specific benchmarks.
Markup vs Margin Calculator
Convert between markup and margin instantly. See both percentages side by side with trade-specific benchmarks for contractors.
HVAC Calculators
Load sizing and refrigerant diagnostics with climate-zone data and pressure-temperature interpolation.
BTU / HVAC Load Calculator
Calculate cooling and heating load by climate zone, insulation, windows, and duct location. Whole-house or room-by-room with tonnage sizing.
Superheat & Subcooling Calculator
Check charge level with PT interpolation for 10 refrigerants including R-454B and R-32. Four-quadrant diagnostic decision tree.
Electrical Calculators
Every calculation cites the specific NEC table and section number. Show-the-math toggles explain the formula in plain English.
Wire Size Calculator
Find the correct wire gauge per NEC 310.16 with temperature derating, bundling adjustment, and 110.14(C) terminal temp enforcement.
Voltage Drop Calculator
Calculate voltage drop percentage for any wire run. Includes reverse-solve for minimum wire size to meet NEC recommendations.
Conduit Fill Calculator
Check NEC Chapter 9 conduit fill compliance for any combination of conductors. Supports EMT, IMC, RMC, PVC, and ENT.
Box Fill Calculator
Calculate junction box fill per NEC 314.16 with conductors, devices, clamps, EGCs, and terminal blocks.
Conduit Bending Calculator
Calculate marks for offsets, saddles, stubs, back-to-back 90s, and kick-90s with interactive SVG diagrams.
EV Charger Installation Calculator
Size wire, breaker, and panel capacity for Level 2 EV charger installs per NEC 625. Includes GFCI requirements and parts list.
Frequently Asked Questions
Are these tools really free?
Yes. Every tool is completely free — no login, no email gate, no ads. We build these tools because they help trade contractors do better work, and we think that earns trust. Intry Systems makes money from our AI dispatch product, not from calculators.
How accurate are the electrical calculators?
All electrical calculators reference the National Electrical Code (NEC) 2023 edition with specific table and section citations. Values are cross-referenced against published manufacturer data from Southwire, Greenlee, and Klein. If you spot an error, contact us — accuracy matters.
Do I need to create an account to use these tools?
No. Every tool works instantly in your browser with zero signup. You can bookmark results or use the share button to generate a link with your inputs pre-filled.
Built by Intry Systems.
We build AI dispatching for trade contractors. Emily answers calls, diagnoses jobs, and builds dispatch briefs — so your techs arrive knowing the job.