Every calculator on this site eventually comes back to these three numbers. Here's what they actually mean, and why sizing anything electrical requires knowing all three, not just one.
The water pipe analogy, briefly
Volts are like water pressure — how hard electricity is being pushed. Amps are like flow rate — how much electricity is actually moving. Watts are the result of both together — the actual power being delivered, similar to how the total force of water hitting something depends on both pressure and flow rate combined.
Why appliances and breakers use different units
Solar panels and generators are almost always rated in watts, since that's the actual power they can deliver or a device consumes. Breakers, fuses, and wire, on the other hand, are rated in amps, since that's what actually generates heat in a conductor. Converting between the two is the single most common calculation in sizing any electrical project — see the watts to amps and amps to watts calculators for both directions.
Ohm's Law ties it all together with resistance
Add resistance (measured in ohms) to the mix, and you get the four core equations that describe any DC circuit — voltage, current, resistance, and power, each solvable from any two of the others.
The Ohm's Law calculator solves for any two known values — useful any time you're reading a nameplate or datasheet and need to fill in a missing number.
Where kWh fits in — the unit that actually shows up on your bill
Watts measure power at an instant; kilowatt-hours (kWh) measure energy used over time — the unit your utility actually bills you in. A 5kW solar array is a power rating (what it can produce at peak); over a day it might produce 20kWh of energy (what actually gets used). Confusing the two is one of the most common mistakes in solar sizing conversations — the kWh to kW calculator converts cleanly between them once you know the time period involved.
Frequently asked questions
Do I need to understand all of this to size a solar system?
Not in depth — our calculators handle the math directly — but knowing the difference between watts and kWh in particular helps you sanity-check any quote or spec sheet you're handed.
Why do some devices list amps instead of watts?
Motors and some appliances are rated by their current draw because that's what determines wire and breaker sizing directly — multiply by voltage to get watts if you need the power figure instead.