Ohm's Law Calculator

Voltage, Current, Resistance & Power

Relationship Wheel

V I R P V=IR

Input Any Two Values

Enter values into any two fields. The other two will be calculated automatically.

Engineering Details

⚡ Fundamental Formulas

The relationship between Voltage, Current, Resistance, and Power is defined by these core equations:

  • V = I × R (Voltage = Current × Resistance)
  • I = V / R (Current = Voltage / Resistance)
  • P = V × I (Power = Voltage × Current)
  • P = I² × R (Heat Loss = Current Squared × Resistance)

🌍 Real-World Engineering Scenarios

1. Drone Current Sensing (Shunt Resistor)

Scenario: Monitoring motor current using a shunt resistor.
Calculation: If a 0.001Ω shunt drops 0.05V:
I = 0.05V / 0.001Ω = 50 Amps

2. Heater & Vape Coil Design

Scenario: Designing a 40W heating element with a 3.7V battery.
Calculation: Using the Power Formula (R = V² / P):
R = 3.7² / 40 ≈ 0.34 Ω

3. Cable Voltage Drop

Scenario: A 10m cable (2Ω round-trip resistance) carrying 1A current.
Calculation: Using Ohm's Law:
V_drop = 1A × 2Ω = 2V Lost If you supply 12V, the camera only gets 10V! This is why selecting the right wire gauge is critical.

⚠️ Common Mistakes

  • Ignoring Power Rating: A 100Ω resistor with 10V across it dissipates 1 Watt (P = V²/R). A standard 1/4W resistor will quickly overheat and fail.
  • Temperature Coefficient: Resistance increases with heat for most metals. In precision circuits, special low-drift resistors are required.

Frequently Asked Questions

Can I use this for AC circuits? Yes, but only for purely resistive loads (like heaters or incandescent bulbs). For loads with inductance (motors) or capacitance, you must calculate Impedance (Z), not just Resistance (R).
Why does my resistor get hot? Current flow generates friction, which manifests as heat. Always ensure your resistor's Power Rating (e.g., 1/4W, 5W) is higher than the calculated Power (P).
What if I have 3 known values? You only need two. If you have three (e.g., V, I, and R) and they don't match the formula V=IR, then either your measurement is wrong or the component is non-ohmic (like a diode or battery).
Is Ohm's Law always valid? No. It applies perfectly to "Ohmic" materials like standard resistors and wires. It does NOT apply directly to non-linear devices like diodes, transistors, or gas discharge lamps.