Voltage vs Current
Voltage is the electrical "pressure" — the potential difference between two points that pushes charges to move. Current is the rate at which charge flows in response. The two are linked through resistance by Ohm's law (V = IR), and both are needed to describe what's happening in a circuit.
Last reviewed on 2026-04-27.
Quick Comparison
| Aspect | Voltage | Current |
|---|---|---|
| What it is | Electrical potential difference | Rate of charge flow |
| Analogy | Water pressure in a pipe | Volume of water flowing per second |
| SI unit | Volt (V) | Ampere (A) |
| Symbol | V or U | I |
| Caused by | Charge separation (battery, generator) | Voltage applied to a conductor |
| Measured with | Voltmeter (in parallel) | Ammeter (in series) |
| Ohm's law | V = IR | I = V/R |
| Power formula | P = VI | P = VI |
Key Differences
1. Pressure versus flow
Voltage is the electrical equivalent of pressure. A battery has voltage between its terminals — a potential difference that wants to push charges from one side to the other through any conductor that connects them.
Current is the equivalent of flow rate. Connect a wire across the terminals and charges actually move; how many flow per second is the current.
2. The water-pipe analogy
Imagine a water tank held high — the height creates pressure, which is voltage. A higher tank means more pressure regardless of how much water flows.
Open a tap at the bottom of the tank and water flows. The flow rate is current. A wider pipe (lower resistance) lets more water flow at the same pressure; a narrow pipe restricts flow.
3. Ohm's law
For most ordinary conductors, voltage, current, and resistance are linked: V = IR. Apply twice the voltage to the same resistor and you get twice the current.
Equivalently, I = V/R. Higher voltage at the same resistance means higher current; higher resistance at the same voltage means lower current.
4. Why both matter for safety
Voltage determines whether current can flow through you in dangerous amounts. Low voltage (a 9 V battery touching skin) doesn't drive enough current through your body to harm. High voltage (mains power, especially industrial) can.
Current through the body is what actually causes damage. Even small currents (around 100 mA through the heart) can be fatal. Voltage matters because it determines current; current is what hurts.
5. Power
Electrical power is the product: P = V × I.
A 12 V battery delivering 5 A produces 60 W of power. The same 60 W could come from 60 V at 1 A, or 6 V at 10 A, or any other combination — same total power, different combinations of voltage and current.
6. Measuring
Voltage is measured between two points — across a component — with a voltmeter, which has high resistance so it draws minimal current.
Current is measured along the path — through a component — with an ammeter, which has very low resistance so it doesn't impede the flow it's measuring.
When to Choose Each
Choose Voltage if:
- Specifying power supplies, batteries, and grid voltages.
- Selecting components rated for specific voltage tolerances.
- Anywhere the "force" pushing electricity matters.
Choose Current if:
- Sizing wires (current-carrying capacity).
- Understanding why a circuit overheats or trips a breaker.
- Specifying loads — appliances are rated by current as well as voltage.
Worked example
A typical UK mains socket provides 230 V. A kettle drawing 10 A from that socket consumes 230 × 10 = 2,300 W. A small lamp drawing 0.1 A from the same socket consumes 23 W. Same voltage, different currents based on how much resistance each appliance presents — and very different power consumption as a result.
Common Mistakes
- "It's the volts that kill you." Current is what causes injury; voltage matters because high enough voltage drives dangerous current. Both contribute, but the immediate damage is from current.
- "More volts is always more power." Only if the current also matches. Power is the product of both.
- "Voltage flows through wires." Voltage exists between two points; current flows along the wire.
- "AC and DC are different in everything." Both have voltage and current; they differ in whether direction reverses (see AC vs DC current).