OhmDeck Electrical Calculators
Fast electrical calculators and beginner-friendly guides for quick planning and sanity checks, built for DIYers, hobbyists, and curious homeowners who want to understand the numbers before anything gets loud.
Why knowing your electrical numbers matters
It is a cold January morning. You plug a space heater into the living room outlet, crank it up to high, and go to make coffee. Ten minutes later the breaker trips. Half the house goes dark. You reset it, plug the heater back in, and it trips again. You start wondering if the heater is broken or if the breaker is wearing out.
The problem is neither. That circuit was already running a lamp, a TV, and a cable box. Add a 1,500-watt space heater and you are pushing more than 15 amps through a 15-amp circuit. The breaker did exactly what it was designed to do: it protected the wiring before anything overheated.
Most home electrical problems come down to a handful of numbers: amps, watts, and volts. Amps measure how much current is flowing through a wire. Watts tell you how much power a device is consuming at any moment. Volts are the pressure that drives the current through the circuit. When you know those three numbers, you can look at any circuit, add up what is plugged into it, and know before anything trips whether you are within the safe limit or creeping past it.
That space heater situation is one of the most common calls electricians take. It is almost never a broken heater or a faulty breaker. It is a homeowner who did not know that their living room circuit was already running near its limit. A 30-second calculation would have caught it.
You do not need to be an electrician to understand your home's electrical load. You just need to know where to look and how to do the math. That is exactly what OhmDeck is built for.
Where to start
If you're new to electrical terms, start here:
How to use OhmDeck
Here is a real example. You want to run a 1,500-watt space heater in the living room. The circuit already has a lamp drawing about 60 watts and a TV pulling around 120 watts. You are not sure if the circuit can handle one more thing. Here is how to check before you plug anything in.
Open the Watts to Amps Calculator. Enter 1,500 watts and 120 volts. The result is 12.5 amps. A 15-amp circuit's safe sustained limit is 80 percent of its rated capacity, which works out to 12 amps. The space heater alone is already over that limit, and you have not counted the lamp or the TV yet.
The practical fix: move the heater to a different circuit, one that is not already loaded, or swap it for a 750-watt model that draws only about 6.25 amps. A quick check before you run a new appliance is a lot easier than resetting a tripped breaker in the dark. Every calculator on OhmDeck works the same way: enter what you know, get a number you can use, and make a smarter decision before anything gets loud.
Common circuit limits at a glance
Here is a quick reference for the most common household circuit ratings and their practical load limits.
| Circuit | Maximum wattage | Safe sustained limit (80%) | Common uses |
|---|---|---|---|
| 15A at 120V | 1,800W | 1,440W | Lighting, outlets, small appliances |
| 20A at 120V | 2,400W | 1,920W | Kitchen circuits, bathroom outlets |
| 30A at 240V | 7,200W | 5,760W | Dryer, water heater, large AC |
| 50A at 240V | 12,000W | 9,600W | EV charger, electric range, subpanel feeder |
| 100A subpanel | Service maximum | Varies by load | Garage workshop, major addition |
Always verify circuit load with a licensed electrician before adding high-draw appliances.
All Calculators
Find out how much power a device uses when you know the current it draws.
Check how many amps an appliance pulls so you can compare it against your circuit rating.
Calculate power output when you know the voltage and current of a circuit or device.
Convert apparent power to current for generators, UPS systems, and commercial equipment.
Convert current back to apparent power for generator and equipment sizing.
Estimate running load, startup headroom, and a practical portable-generator size for home backup planning.
Find the current draw of a device rated in kilowatts, useful for EV chargers and large appliances.
Convert current back to kilowatts for power output calculations.
Quickly shift between watts and kilowatts when comparing appliance ratings or utility bills.
Estimate how much energy an appliance uses over time, useful for understanding your electric bill.
Calculate what an appliance costs to run per day, month, or year based on your utility rate.
Solve for voltage, current, or resistance when you know any two of the three values.
Calculate power for standard residential circuits using voltage and current.
Calculate power for commercial and industrial three-phase electrical systems.
Resistor Color Code Calculator
Decode resistor color bands to find resistance values for electronics projects.
Estimate the right breaker size for a circuit based on the connected load.
Get a common wire-size starting point based on amps, distance, voltage, and conductor material.
Convert Level 2 charger power into charging amps and the minimum breaker size.
Check how much voltage is lost over a long wire run so you can size conductors correctly.
Extension Cord Size Calculator
Choose a practical temporary cord gauge from amps, length, and voltage-drop-aware planning.
Guides for homeowners and DIYers
The calculators handle the math. These guides handle the questions that come before the math.
Why Does My Breaker Keep Tripping?
Find out what your tripping pattern is telling you and when to call an electrician.
Can You Run a Space Heater on an Extension Cord?
A practical safety answer for one of the most common cold-weather cord questions, with direct-outlet guidance and the rare heavy-cord exception.
Learn where to find the real wattage number before you overload a circuit.
Running Watts vs Starting Watts
See why refrigerators, sump pumps, and other motor loads can force a larger generator than the running load suggests.
What Size Generator for a Refrigerator?
A practical outage-planning answer for one fridge, with startup surge context and the right calculator next step.
How to Read Your Electric Bill
Understand the numbers on your bill and spot what is driving your costs up.
Start here if you want to understand volts, amps, and watts in plain language before using any calculator.
What Wire Size for a Level 2 EV Charger?
Common starting points for 32A, 40A, and 48A charging, plus what changes the answer on a longer run.
See when run length turns a normal wire-size answer into the next larger conductor.
Can a 100A Panel Handle an EV Charger?
A practical look at smaller chargers, spare capacity, and when a load calculation or upgrade is needed.
About OhmDeck
OhmDeck is built by home electrical enthusiasts and DIYers who got tired of looking up the same numbers across five different sites. Every calculator is checked against real-world values and every guide is written to answer the questions homeowners actually ask, not the questions textbooks think they should ask. If you find an error or have a question that is not answered here, use the contact page to let us know.
OhmDeck provides general informational estimates only and does not constitute electrical, engineering, or legal advice. Always verify requirements with the applicable electrical code and consult a qualified licensed electrician before performing electrical work. Read our full disclaimer before relying on any estimate.