Ohm's Law Calculator & Tools

Ohm's Law Calculator & Tools is a fast, accurate electrical calculator for electricians, installers, technicians, students and hobbyists. Enter any two of voltage, current, resistance and power, and the other two appear instantly while you type. There is no Calculate button and no jumping between screens.

Live Ohm's law calculator

Fill in any two of the four values and the app works out the rest as you type. It also shows you which formula it applied, with your numbers substituted in — for example R = V / I = 12 V / 0.5 A = 24 Ή. Calculated values are highlighted so it is always clear what you entered and what the app derived. Do one calculation after another without clearing anything; a long press clears a single field.

Units that do not break

Every value is stored in base SI units, and the prefix selector is purely a display layer. Switching between , m, k and M relabels the number instead of corrupting it. Results pick a sensible prefix automatically, so 0.0047 Ή is shown as 4.7 mΉ. Both a dot and a comma work as the decimal separator.

The tools you actually reach for

• Power and kVA: DC, AC single-phase and AC three-phase, with power factor and reverse calculations
• Resistor colour code, both directions: pick the bands to get the value, or enter a value to get the bands. 3, 4, 5 and 6 band layouts, tolerance, temperature coefficient and the min/max range
• SMD resistor markings: 3-digit, 4-digit, EIA-96 and decimal-point codes
• Series and parallel networks for resistors, capacitors and inductors, up to ten components
• Voltage drop, in both metric (mm, ΁) and imperial (AWG, circular mils) branches, single-phase and three-phase, copper and aluminium
• Wire size: AWG to mm and back, conductor diameter, circular mils, and the minimum cross-section for an acceptable voltage drop
• LED series resistor, including LED strings, with the nearest E24 value and a recommended power rating
• Energy cost: kWh and running cost per day, month and year
• Unit converter for voltage, current, resistance, power, energy, capacitance, inductance, frequency and charge
• An offline formula reference: the Ohm's wheel, AC formulas, cable formulas, the E12/E24/E96 preferred-value series, colour code tables, symbols and prefixes

History that remembers exactly what you did

Save a result and it is stored with its inputs, its units and the formula that produced it. Search your history, pin the calculations you keep coming back to, copy or share a result as text, and tap any entry to reopen it in its calculator with the exact values it was saved with.

Built the way a tool should be

• Works offline. Every calculation runs on your device.
• No subscriptions. No paywall. No locked "Pro" features.
• Light, dark and system themes.
• Adapts to tablets with a two-column layout.
• 30+ languages.

Accuracy

Every formula is covered by unit tests with known control values, and nothing is rounded until it is displayed. If a combination of inputs would divide by zero, you get a clear message rather than a wrong number.

A note on the reference data

Results are provided for reference and education. They do not replace national wiring regulations, manufacturer data, or a qualified design calculation. The ampacity and voltage drop figures in this app are indicative values, not code requirements — always check the rules that apply where you work.

Questions or a formula you would like added? Write to zoryatechstudio@gmail.com.

Recent changes:
First release.

Ohm's law, power, resistor colour codes, voltage drop, wire size, LED, kWh.