Education & Student
Ohms Law Calculator
Use Ohm’s law V = I × R to find voltage, current or resistance for a passive-resistor model. Choose the unknown and enter the two labeled quantities in volts, amperes or ohms.
This local calculator solves one of V = IR, I = V/R or R = V/I. It accepts signed voltage and current with a consistent polarity convention and nonnegative resistance. Power is a separate calculation using P = VI.
About this calculator
Select the unknown before entering values so the field labels match the required quantities. For example, 12 V across 4 Ω gives current 3 A. The corresponding power is 36 W by a separate multiplication, P = VI; this form returns the selected V, I or R result.
How to use
- Choose which quantity to solve for: V, I, or R.
- Enter the first labeled quantity, converting mA to A or kΩ to Ω when needed.
- Enter the second labeled quantity in its displayed unit.
- Press Calculate to read the result.
Why use Ohms Law Calculator
Fast
Calculations run in your browser. No round trip to a server.
Private
Your inputs never leave your device. Nothing is uploaded.
Free
No signup, no paywall, no ads-in-results, no watermarks.
Accurate
Uses standard formulas for quick educational estimates; check critical results before relying on them.
Mobile-ready
Optimised for phones, tablets, and desktops alike.
Transparent
Honest disclaimers wherever browser limits or regional rules apply.
Common uses
Use it for quick what-if calculations
Use it when comparing two scenarios
Use it for tutoring and study groups
Use it for cross-checking a measurement
Use it when checking a homework answer
Use it before a practical assessment
Technical notes
The model uses a passive ohmic resistance. Voltage and current may be signed; when solving R = V/I, their nonzero signs must agree to give nonnegative resistance. Division requires R > 0 for current mode or I ≠ 0 for resistance mode. Other zero results are allowed. Very small values use scientific notation; arithmetic overflow and underflow are rejected. The form does not model nonlinear components, temperature changes, impedance or a complete circuit, and does not calculate power automatically.
Results assume ideal conditions and consistent units, so convert your inputs to the units shown before calculating.
The tool works offline once loaded, since every computation is client-side.
FAQ
Which quantities should I enter?
They depend on what you solve for: for V you enter current then resistance; for I you enter voltage then resistance; for R you enter voltage then current.
What is Ohm's law?
For an ohmic component at unchanged physical conditions, voltage is proportional to current, with V = I × R. A single V/I ratio does not prove that resistance stays constant as operating conditions change.
Which zero values and signs are supported?
Current mode requires positive resistance. Resistance mode requires nonzero current and a voltage with a consistent sign. Voltage mode permits signed current and nonnegative resistance. A zero numerator can give a zero result, but zero divisors and negative passive resistance are rejected.
Does the Ohms Law Calculator send my data to a server?
No. The Ohms Law Calculator runs entirely in your browser, so nothing you enter is uploaded, stored, or shared.
Worked example
Ohm's law: 12 V across 4 Ω draws I = 12 ÷ 4 = 3 A, dissipating P = 12 × 3 = 36 W.