Electrical Calculators

Electricity follows strict rules, which makes it perfect for calculators. Every circuit question comes down to the same four quantities — voltage, current, resistance and power — and one simple relationship between them. Whether you are an electrician sizing a circuit, a student working through Ohm’s law homework, or a hobbyist building an electronics project, getting these numbers right matters: too much current burns components, and too little means the circuit never works. This page gathers the electrical calculators on all-calculators.info so you can solve for any missing quantity in seconds, with the formula and a worked example under every tool. The tools here are deliberately simple: enter what you know, get what you don’t, and check the worked example to understand why. Every calculator is free, works on your phone or computer, and needs no sign-up.

Ohm’s law is the foundation: voltage equals current times resistance (V = I × R), and electrical power is voltage times current (P = V × I). Once you know any two values, the other two follow — which is exactly what the calculator below does for you, showing every step of the working. It is the single most useful relationship in practical electronics: learn it once and you will use it forever.

Popular Calculators

• Battery Life Calculator — work out how long a battery will power a device.
• LED Resistor Calculator — work out the resistor an LED circuit needs.
• Power Calculator — work out electrical power from voltage and current.
• Resistor Color Code Calculator — read a resistor’s value from its colour bands.
• Torque Calculator — work out torque from force and distance.
• Voltage Drop Calculator — work out the voltage lost along a cable run.
• Wire Size Calculator — work out the wire gauge a circuit needs.

How to Choose the Right Calculator

Ohm’s Law Calculator

The Ohm’s Law Calculator is the heart of this category: give it any two of voltage, current and resistance and it works out the rest, plus the power. Use it when you need to find the missing quantity — the current through a resistor, the voltage across a load, or the resistance needed to keep current within safe limits. It also shows power, because watts are what heat components: a resistor passing too much current doesn’t just misbehave, it burns. Students can check homework answers here, and hobbyists can sanity-check a circuit design before soldering anything. Electricians use the same relationship in bigger circuits too: it is how you check that a breaker won’t trip and that a wire won’t overheat. The calculator handles the arithmetic; your job is knowing which two values you have. If you already know all three quantities and only want the power, the tool still shows it — no separate calculator needed. Run the numbers here first; components are cheaper unburnt.

Good to Know

Four electrical habits:

• Double-check units: volts, amps and ohms must be consistent — 1,000 milliamps is 1 amp, and mixing them up throws every answer by a factor of a thousand. Remember the prefixes: milli means a thousandth, kilo means a thousand.
• Mind the power rating: a resistor’s wattage limit matters as much as its resistance; the calculator’s power figure tells you whether the part will survive.
• Measure before you trust: real components vary from their printed values, so verify with a multimeter when a circuit misbehaves.
• Safety first: these calculators do the maths, but they don’t make a circuit safe — mains voltage can kill, so leave household wiring to a qualified electrician.

Frequently Asked Questions

What is Ohm’s law in simple terms?

It says that current through a resistor equals voltage divided by resistance (I = V ÷ R). Double the voltage and the current doubles; double the resistance and the current halves. Everything on this page builds on that one idea, so it is worth memorising.

How do I calculate electrical power?

Multiply voltage by current (P = V × I). A 12-volt circuit drawing 2 amps uses 24 watts — checkable in seconds. The Ohm’s Law Calculator shows the power alongside the other answers, so you never have to work it out separately.

What happens if I use the wrong resistor?

Too little resistance lets too much current through, which overheats and destroys components; too much resistance starves the circuit so it barely works. Calculate first with the tool, then build — guessing with resistors is an expensive habit.

Are these calculators free?

Yes. Every calculator on this page is free, with no sign-up, and works on your phone or computer.

Why use these calculators?

Every calculator on this page is free, works on your phone or computer, and shows the formula and a worked example under the tool — so you can see exactly how your answer was calculated, not just the answer.