What Is Voltage? A Clear Explanation for Beginners

Voltage is the difference in electric potential between two points in a circuit. It is the force that pushes electric charge (current) through a conductor. Without voltage, no current flows. Voltage is measured in volts (V) and is sometimes called electromotive force (EMF), potential difference, or electric pressure.

How voltage works

Every electrical circuit needs a source of voltage to function. A battery, power supply, or wall outlet provides voltage — it creates a difference in electric potential between its two terminals. This difference is what drives electrons through the wires and components in the circuit.

Think of voltage like water pressure in a pipe. The pressure itself doesn't mean water is moving — it means there is a force available to push water when the valve opens. Similarly, a 9V battery has 9 volts of electrical pressure across its terminals whether or not anything is connected to it.

When you connect a circuit to a voltage source, current begins to flow from the high-potential terminal (positive) through the circuit to the low-potential terminal (negative). The amount of current that flows depends on the resistance in the circuit, as described by Ohm's Law.

The voltage formula

The fundamental relationship between voltage, current, and resistance is Ohm's Law:

V = I × R

Where:

• V = voltage in volts (V)
• I = current in amperes (A)
• R = resistance in ohms (Ω)

This means:

• If you know current and resistance, calculate voltage: V = I × R
• If you know voltage and resistance, calculate current: I = V / R
• If you know voltage and current, calculate resistance: R = V / I

You can also calculate voltage using power: V = P / I, where P is power in watts. Try these calculations instantly with our Ohm's Law Calculator.

Voltage in series and parallel circuits

How voltage behaves depends on whether components are connected in series or parallel.

Voltage in a series circuit

In a series circuit, the total source voltage is divided across each component. The voltage drops across all components add up to the source voltage. For example, if a 12V battery powers three equal resistors in series, each resistor gets a 4V drop.

V_total = V₁ + V₂ + V₃ + ...

This is called the voltage divider effect. See our voltage drop guide and voltage divider calculator for worked examples.

Voltage in a parallel circuit

In a parallel circuit, the voltage across every branch is the same and equals the source voltage. If a 12V battery powers three resistors in parallel, each resistor has 12V across it regardless of its resistance value.

V_total = V₁ = V₂ = V₃

Types of voltage

DC voltage (direct current)

DC voltage maintains a constant polarity — the positive and negative terminals stay the same. Batteries, USB chargers, solar cells, and most electronic circuits use DC voltage. A 9V battery always provides 9 volts in the same direction.

AC voltage (alternating current)

AC voltage reverses polarity periodically, typically as a sine wave. Wall outlets provide AC voltage — 120V at 60 Hz in North America, 230V at 50 Hz in most of Europe. The voltage swings between positive and negative values many times per second.

Learn more about the differences in our AC vs DC guide.

Common voltage levels

How to measure voltage

Voltage is measured with a voltmeter or a multimeter set to voltage mode. Unlike current measurement (which requires breaking the circuit), voltage is measured in parallel — you place the probes across the component or points you want to measure without disconnecting anything.

Steps to measure voltage

1. Set your multimeter to the appropriate voltage mode — DC (V⎓) for batteries and electronics, AC (V~) for wall outlets.
2. If your meter is not auto-ranging, select a range higher than the expected voltage.
3. Touch the red probe to the higher-potential point (positive side).
4. Touch the black probe to the lower-potential point (negative side or ground).
5. Read the voltage on the display.

If you get a negative reading, your probes are reversed — the red probe is on the lower-potential side. This won't damage the meter; just swap the probes.

Voltage drop

As current flows through a component, some voltage is "used up" — this is called a voltage drop. Every resistor, LED, motor, and wire in a circuit creates a voltage drop. The sum of all voltage drops in a series circuit equals the source voltage (this is Kirchhoff's Voltage Law).

Voltage drop matters in practice: if you're powering an LED from a 5V Arduino pin, the LED drops about 2V and you need a resistor to drop the remaining 3V. Use our LED resistor calculator to find the right resistor value.

For a detailed walkthrough, read our guide to calculating voltage drop across resistors.

Voltage vs current vs resistance

These three properties are connected by Ohm's Law: V = I × R. If you increase voltage while resistance stays the same, current increases. If you increase resistance while voltage stays the same, current decreases.

Common mistakes with voltage

• Confusing voltage with current. Voltage is the push; current is the flow. A static shock is high voltage (thousands of volts) but extremely low current, which is why it stings but doesn't kill you.
• Assuming higher voltage means more danger. It's the current through your body that causes harm, not voltage alone. However, higher voltage can push more current through the body's resistance, so high voltage is still dangerous.
• Forgetting voltage drop. In a series circuit, each component uses some voltage. If you chain too many LEDs in series, the last ones won't light up because there's no voltage left.
• Measuring voltage in series instead of parallel. A voltmeter must be connected across (in parallel with) the component being measured, never in series with it.

Summary

Voltage is the electrical potential difference between two points, measured in volts. It is the driving force behind every electrical circuit — without it, no current flows. Voltage relates to current and resistance through Ohm's Law (V = I × R). In series circuits, voltage divides across components; in parallel circuits, voltage is the same across all branches. You measure voltage in parallel using a multimeter.