PickettOhm

Interactive Ohm's Law Calculator & Guide

Ohm's Law Calculator — Voltage, Current & Resistance

V
I
R

🔋 Ohm's Law Formulas

V
V = I × R
Voltage equals Current times Resistance

Calculate Voltage

V=? R I
Example:
Current (I) = 2A
Resistance (R) = 5Ω
V = 2A × 5Ω = 10V
I
I = V ÷ R
Current equals Voltage divided by Resistance

Calculate Current

12V 6Ω I=?
Example:
Voltage (V) = 12V
Resistance (R) = 6Ω
I = 12V ÷ 6Ω = 2A
R
R = V ÷ I
Resistance equals Voltage divided by Current

Calculate Resistance

9V R=? 3A
Example:
Voltage (V) = 9V
Current (I) = 3A
R = 9V ÷ 3A = 3Ω

⚡ Calculate Voltage

V = I × R
A
Ω

⚡ Calculate Current

I = V ÷ R
V
Ω

⚡ Calculate Resistance

R = V ÷ I
V
A

⚡ Power Formulas (Watts)

Power (P) measures the rate of energy transfer, measured in Watts (W)

P = V × I
Power = Voltage × Current

Power from Voltage & Current

12V P=? 2A
Example:
Voltage (V) = 12V
Current (I) = 2A
P = 12V × 2A = 24W
P = I² × R
Power = Current² × Resistance

Power from Current & Resistance

V 10Ω P=? 3A
Example:
Current (I) = 3A
Resistance (R) = 10Ω
P = 3² × 10Ω = 9 × 10 = 90W
P = V² ÷ R
Power = Voltage² ÷ Resistance

Power from Voltage & Resistance

24V 12Ω P=? I
Example:
Voltage (V) = 24V
Resistance (R) = 12Ω
P = 24² ÷ 12Ω = 576 ÷ 12 = 48W

Voltage (V)

V
  • Electrical pressure or potential difference
  • Measured in Volts (V)
  • Pushes electrons through a circuit
  • Like water pressure in a pipe
  • Symbol: V or E

Current (I)

I
  • Flow of electric charge
  • Measured in Amperes (A)
  • Rate of electron flow
  • Like water flow in a pipe
  • Symbol: I

Resistance (R)

R
  • Opposition to current flow
  • Measured in Ohms (Ω)
  • Restricts electron movement
  • Like friction in a pipe
  • Symbol: R

🔌 Electricity Basics for Beginners

Let's understand electricity using simple terms!

⚡ Voltage (V)

What is it? Voltage is the electrical "pressure" that pushes electrons through a circuit. It's measured in Volts (V).

Think of it like: The height of a waterfall. The higher the waterfall, the more pressure the water has when it falls.

💡 Real Life: A 9V battery has more "push" than a 1.5V battery, just like a tall waterfall has more force than a short one!

🌊 Current (I)

What is it? Current is the flow of electricity through a wire. It's measured in Amperes or Amps (A).

Think of it like: The amount of water flowing through a pipe. More current means more electricity is flowing.

💡 Real Life: A phone charger uses about 1-2 Amps, while a microwave might use 10 Amps. More amps = more power flowing!

🚧 Resistance (R)

What is it? Resistance is anything that slows down or opposes the flow of electricity. It's measured in Ohms (Ω).

Think of it like: A narrow pipe or rocks in a stream that slow down water flow.

💡 Real Life: LED bulbs have high resistance (they don't need much current), while a short circuit has almost zero resistance (dangerous - too much current flows!)

💪 Power (P)

What is it? Power is how much energy is being used or produced per second. It's measured in Watts (W).

Think of it like: How much work is being done. More watts means more energy is being used.

💡 Real Life: A 60W light bulb uses 60 watts of power. A 1000W microwave uses much more energy (and heats your food faster!)

💧 The Water Pipe Analogy

Imagine electricity flowing through wires like water flowing through pipes:

⛲
Voltage

Water Pressure
(How hard it pushes)

🌊
Current

Water Flow
(How much flows)

🚰
Resistance

Pipe Width
(Narrow = more resistance)

⚙️
Power

Work Done
(Turning a water wheel)

🎯 Ohm's Law says: If you increase the voltage (pressure), more current (water) will flow. But if you increase resistance (make the pipe narrower), less current will flow!

🔌 Practical Calculators

Essential calculations for everyday circuit design

⚡ Voltage Divider

Vout = Vin × R2 ÷ (R1 + R2)

V
Ω
Ω

💡 LED Resistor Calculator

R = (Vsupply − Vforward) ÷ ILED

V
mA

🔗 Series & Parallel Resistors

⚖️ Wheatstone Bridge

Balanced when R1/R2 = R3/R4. Find unknown resistance.

Ω
Ω
Ω

🎨 Resistor Colour Code Decoder

Decode 4-band and 5-band resistor markings

4-Band Resistor

Select colours above

5-Band (Precision) Resistor

Select colours above

🔁 Kirchhoff's Laws

The two fundamental laws governing all circuit analysis

KCL — Kirchhoff's Current Law

ΣIin = ΣIout

The sum of all currents entering a node equals the sum of all currents leaving it. Charge cannot accumulate — what flows in must flow out.

  • Based on conservation of charge
  • Applies at every node (junction)
  • Used to find unknown branch currents
  • Example: 3A + 2A in → 5A out ✓

KVL — Kirchhoff's Voltage Law

ΣV = 0 (around any loop)

The sum of all voltage rises and drops around any closed loop equals zero. Energy supplied equals energy consumed.

  • Based on conservation of energy
  • Applies to any closed loop
  • Voltage rises (sources) = voltage drops (loads)
  • Example: 9V − 3V − 6V = 0 ✓

🔢 KVL Loop Solver — Find Unknown Voltage

Enter known voltages in the loop (use − for drops, + for sources). The solver finds the missing value.