Marcus Vance
Master Electrician · Austin, TX
The commercial load calculations saved me hours on my last blueprint review. The voltage drop results perfectly matched my manual NEC formulas.
Voltage DropFor electricians & homeowners
Free electrical calculators, built on
the NEC.
Voltage drop, wire size, conduit fill and more — accurate tools that show the formula behind every result. Precise enough for licensed electricians, clear enough for homeowners. No signup.
Voltage drop · live
scope
RUN120 ft
DROP2.6%
↔ Move across — reads the drop at any wire run, like the calculator does.
NEC-based
Built to the current code
Transparent
Every tool shows its formula
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All electrical calculators
- Voltage Drop Calculator — check conductor loss against the NEC 3% limit.
- Wire Size Calculator — right conductor gauge for the load and length.
- Circuit Breaker Size Calculator — size the breaker to the circuit's ampacity.
- Conduit Fill Calculator — check conductor fill against NEC conduit limits.
- Watt-to-Amp Calculator — convert watts to amps at any voltage.
- Ampere Calculator — find current from watts, volts and resistance.
- Ohm's Law Calculator — solve voltage, current, resistance or power.
- Power Factor Calculator — compare real vs apparent power and correct it.
- Electrical Load Calculator — total a panel's demand load in amps.
- Generator Size Calculator — size backup power to your home's load.
- Solar Panel Calculator — estimate array size for your energy use.
Why Electrical Calcs
Free electrical calculators, built for real work
A focused set of online electrical calculators that turn the formulas behind everyday electrical work into fast, accurate answers — and show you exactly how each result was reached.
What these calculators do
Every job runs on the same handful of calculations. Our electrical calculators cover the ones that come up most: the voltage drop calculator for keeping a run within the NEC limit, the conduit fill calculator for packing a raceway safely, and the wire size calculator for picking the right conductor gauge. Breaker sizing, load totals, watt-to-amp conversions and more sit alongside them — one hub instead of a dozen scattered tools.
Built on the NEC — and verifiable
Electrical work is safety work, so accuracy isn't optional. These NEC electrical calculators are built to the current National Electrical Code, and every tool shows the formula it used and cites the relevant NEC article — so you can check the math, not just trust it. No black boxes, no guesswork. When a result sits close to a code limit, the tool flags it instead of quietly passing.
For electricians and homeowners alike
For licensed electricians, these are quick, reliable electrical calculators that confirm a sizing decision in seconds on the truck or at the panel. For homeowners and DIYers, each one explains what the numbers mean in plain language, so you understand a circuit before you touch it. Free to use, no signup, no account — the full set runs right in your browser.
Most used tool
Ready to run the numbers?
Start with the voltage drop calculator — check any wire run against the NEC 3% limit in seconds, with the formula shown.
How we build & verify
Why you can trust these calculators
Electrical work is safety work, so every calculator here is built to the current National Electrical Code (NEC) and shows its working. Each tool displays the exact formula it used and cites the relevant NEC article, so the result is something you can verify — not just trust. We don't publish fake reviews or invented credentials; our credibility comes from transparent, checkable math and clearly stated limits.
These tools are a guide for planning and learning — not a substitute for a licensed electrician or the current edition of the NEC. Always confirm against local code and have work inspected where required.
NEC-VERIFIED · 001
Verification record
METHOD / NEC-BASED
Code basis
Built to the current NEC edition
Transparency
Formula & NEC article shown per tool
Limits
Near-code results flagged, not hidden
No fake reviews · no invented credentials
Verified
Trusted on the job
Electricians and homeowners rely on these tools
Real feedback from licensed pros, inspectors and DIYers who use these calculators in the field.
Elena Rostova
Electrical Engineer · Chicago, IL
An excellent, highly reliable tool for quick sanity checks before stamping plans. The motor circuit calculations are completely accurate to code.
Electrical Load
Sarah Jenkins
Electrical Contractor · Columbus, OH
I use the conduit fill calculator right on my phone while out on job sites. It keeps my crew compliant and prevents us from failing rough-in inspections.
Conduit Fill
Tom Henderson
Homeowner / DIYer · Calgary, AB
I wired my new backyard workshop safely without drowning in confusing math. It made calculating the subpanel feeder wire size incredibly simple.
Wire Size
Common questions
Electrical questions, answered
NEC-grounded answers to what people ask most — each one routes you to the tool that does the math.
ConversionsHow many amps does a refrigerator use?
Most household refrigerators draw about 3 to 6 amps while running at 120 volts, but the compressor briefly surges much higher at startup. That inrush is why fridges sit on a dedicated 15- or 20-amp circuit.
ConversionsHow do I calculate amps from watts and volts?
Current equals power divided by voltage: amps = watts ÷ volts. So a 1,200-watt load on a 120-volt circuit draws 10 amps. Three-phase and power-factor cases adjust the formula slightly.
Loads & backupWhat size generator do I need for my house?
It depends on which loads you want to run at once. Backing up the essentials — fridge, a few lights, furnace fan, outlets — usually needs a 5,000–7,500-watt generator, while whole-house coverage with central AC often calls for 10,000+ watts.
Wire & circuitWhat size wire do I need for a 30-amp circuit?
A 30-amp circuit typically uses 10-gauge copper wire under the NEC's standard ampacity rules. Long runs may need an upsized conductor to hold voltage drop within limits.
Wire & circuitWhat is an acceptable voltage drop?
The NEC recommends keeping voltage drop to a maximum of 3% on a branch circuit, and 5% across the feeder and branch combined. These are recommendations, not hard rules, but staying under them protects performance and efficiency.
Wire & circuitHow do I size a circuit breaker?
A breaker protects the wire, so it's sized to the conductor's ampacity — never above what the wire can safely carry. Continuous loads are figured at 125% of their rated current.
ConduitHow full can a conduit be?
The NEC limits conduit fill by the number of conductors: 53% for a single wire, 31% for two, and 40% for three or more. Staying within these keeps wires from overheating and makes them easier to pull.
Loads & backupHow do I calculate the electrical load for a house?
Residential load is totalled using NEC Article 220: add general lighting and receptacle loads, then small-appliance, laundry, and the larger of the heating or cooling load, plus fixed appliances — applying the code's demand factors.
ConversionsWhat is a good power factor?
Power factor is the ratio of real power to apparent power, from 0 to 1. A value of 0.95 or higher is considered good; below about 0.8 is poor and can mean wasted energy and utility penalties on larger services.
Loads & backupWhat size solar system do I need?
It comes down to your energy use and local sun hours. Take your average daily kilowatt-hours, divide by usable sun hours, and add headroom for real-world losses to get the array size in kilowatts.
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