Ohms Law Resistance Calculator
Find electrical resistance from voltage and current with Ohm's law. Enter volts and amps to get R = V/I instantly, with step-by-step work. Free, no signup.
What Is an Ohm's Law Resistance Calculator?
An Ohm's law resistance calculator determines how much a component opposes current when you know the applied voltage and measured current. Resistance is fundamental for choosing resistors, analyzing circuits, and troubleshooting unexpected current draw.
Resistance Formula
Rearranging Ohm's law gives resistance from voltage and current:
$$R = \frac{V}{I}$$If 9 V produces 0.15 A, the load resistance is 60 Ω. Higher resistance means less current for the same voltage.
When to Calculate Resistance
Engineers use this when characterizing unknown loads, verifying pull-up resistor values, or checking whether a heating element still meets spec. Combine the result with a power calculation to estimate heat dissipation.
Related tools: Ohm's Law Current Calculator, Ohm's Law Power Calculator, and Ohm's Law Calculator.
Frequently Asked Questions
How do I measure resistance in practice?
A multimeter in ohms mode applies a small test voltage and reports resistance directly. This calculator is useful when you already know operating voltage and current under load.
Does temperature affect resistance?
Yes. Most metals increase resistance as they heat up. Carbon and thermistors can decrease resistance with temperature. Lab measurements at room temperature may differ from hot operating values.
What if current is zero?
Zero current with nonzero voltage implies infinite resistance, such as an open circuit. The calculator requires positive current to produce a finite result.
Can I find resistance from power?
Yes. From P = V²/R you get R = V²/P, or from P = I²R you get R = P/I². Use whichever pair of known values you have.
What is the difference between resistance and impedance?
Resistance applies to DC and purely resistive AC circuits. Impedance includes reactive effects from capacitors and inductors and is used for AC analysis.
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