liminfoCircuit Calculator
Free web tool: Circuit Calculator
Circuit Calculator
V = I × R. Select which variable to calculate.
About Circuit Calculator
The Circuit Calculator is a four-function electronic circuit tool covering the most fundamental calculations in DC circuit analysis. The Ohm's Law tab implements V = I × R, allowing you to select which of the three variables (Voltage, Current, or Resistance) you want to solve for and then input the other two. The Power tab applies P = V × I for solving power, voltage, or current given the remaining two quantities. Both tabs update results in real time using JavaScript's useMemo hook, so results appear as you type without requiring a submit button.
The Series Resistor tab computes total resistance for any number of resistors connected in series using R_total = R₁ + R₂ + … + R_n. The Parallel Resistor tab uses the reciprocal formula 1/R_total = 1/R₁ + 1/R₂ + … + 1/R_n for parallel networks. In both cases you enter resistor values as a comma-separated list, and the tool automatically parses each value, filters out non-numeric entries, and displays the total resistance along with the count of resistors. This makes it straightforward to verify complex multi-resistor networks without a physical calculator.
Electronics students, hobbyists working with Arduino or breadboard circuits, electricians, and engineers performing quick back-of-envelope checks will find this tool particularly useful. All calculations run entirely in the browser without any server interaction. The interface uses tabs for clean organization and supports both desktop and mobile use with responsive grid layouts. Dark mode is fully supported throughout, making it comfortable to use in any lighting environment.
Key Features
- Ohm's Law solver: select V, I, or R as the unknown and enter the other two to get an instant result
- Power calculator: solve for P (watts), V (volts), or I (amps) using P = V × I
- Series resistor calculator: R_total = R₁ + R₂ + … for any number of resistors
- Parallel resistor calculator: 1/R_total = 1/R₁ + 1/R₂ + … with reciprocal sum formula
- Comma-separated input for multi-resistor networks — supports any quantity of resistors
- Resistor count display alongside total resistance for network verification
- Real-time calculation with instant result display as inputs change
- 100% client-side processing — no data sent to any server, works offline
Frequently Asked Questions
How does the Ohm's Law calculator work?
Select which variable you want to calculate — Voltage (V), Current (I), or Resistance (R) — using the three buttons. The two input fields for the other variables will appear. Enter your known values and the result is displayed immediately using the formula V = I × R (or its algebraic rearrangements: I = V/R and R = V/I).
What is the difference between series and parallel resistance?
In a series circuit, resistors are connected end-to-end and the total resistance is the sum of all individual resistances (R_total = R₁ + R₂ + R₃). In a parallel circuit, resistors share the same two nodes and the total resistance is always less than the smallest individual resistor, calculated using the reciprocal formula: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃.
How do I enter multiple resistors for the series or parallel calculator?
Type the resistor values separated by commas in the input field, for example: 100, 220, 470. Spaces around commas are optional. The tool automatically parses the list, filters out any non-numeric entries, and calculates the total resistance from all valid positive values.
Can I mix resistors of very different magnitudes, like 10 Ω and 10 kΩ?
Yes, but you must use consistent units. Enter all values in ohms — so 10 kΩ should be entered as 10000. The result will also be in ohms. The tool displays up to 6 significant figures, so even small parallel combinations where one resistor dominates will be computed accurately.
Why does the power calculator have three modes instead of one formula?
P = V × I can also be written as P = V²/R or P = I²R using Ohm's Law substitutions. However, this tool deliberately keeps it simple with only P = V × I, avoiding the need to enter resistance. If you need P from V and R (or from I and R), first use the Ohm's Law tab to find the missing quantity, then switch to the Power tab.
What units does the circuit calculator use?
Voltage is in volts (V), current in amperes (A), resistance in ohms (Ω), and power in watts (W). All results are shown to 6 significant figures using JavaScript's toPrecision(6), which balances precision with readability. For very large or very small values you may want to convert units (e.g., kΩ to Ω, mA to A) before entering them.
Is this calculator suitable for AC circuit analysis?
No, this tool handles DC circuit calculations only. The Ohm's Law and power formulas apply to direct current (DC) or to resistive elements in AC circuits (where impedance equals resistance). For reactive AC circuits involving inductors and capacitors, you would need to work with impedance (Z), reactance (X), and complex phasors, which are not covered here.
Can I use this for LED current limiting resistor calculations?
Yes, the Ohm's Law tab is perfect for this. For an LED with a forward voltage of 2V powered by a 5V supply with a desired current of 20mA: the voltage across the resistor is 5V - 2V = 3V, so set mode to 'Solve R', enter V = 3 and I = 0.02 (amperes), and the result is R = 150 Ω.