Volt
Definition
The volt (symbol V) is the SI unit of electrical potential difference (voltage), representing the pressure that pushes electric charges through a conductor. One volt is defined as the potential difference that moves one ampere of current against one ohm of resistance. Standard US household voltage is 120V for regular outlets and 240V for large appliances (dryers, ranges, AC units). Automotive systems use 12V DC. Industrial power is typically 208V, 277V, or 480V three-phase. Voltage is the 'push' in the water analogy — higher voltage pushes more current through a given resistance.
Why is Volt Important?
In electrical engineering and everyday applications, Volt is a fundamental concept for understanding how electrical systems work. Whether you are an engineer designing circuits, an electrician sizing wires, or a homeowner estimating energy costs, this metric is essential for safety, efficiency, and accurate calculations.
Our electrical conversion calculators help you quickly convert between units and verify calculations, reducing errors and saving time in both professional and DIY electrical work.
What is a Volt?
The volt (symbol V) is the SI unit of electrical potential difference (voltage) — the "pressure" that pushes electric charges through a conductor. One volt drives one ampere through one ohm of resistance. Voltage is the electromotive force that makes current flow, just like water pressure makes water flow through pipes.
Standard Voltages
| System | Voltage | Type | Use |
|---|---|---|---|
| USB devices | 5V | DC | Phones, tablets, accessories |
| USB-C PD / laptops | 20V | DC | Fast charging, laptop power |
| Automotive | 12V | DC | Cars, RVs, marine electronics |
| Solar panels | 18–45V | DC | Residential solar (per panel) |
| US household | 120V | AC | Standard outlets (NEMA 5-15) |
| US large appliances | 240V | AC | Dryers, ranges, AC, EV chargers |
| Commercial (US) | 208V / 277V / 480V | 3-phase AC | Office buildings, industrial |
| International | 220–240V | AC | Most countries except US/Japan |
Voltage, Current, and Resistance (Ohm's Law Triangle)
| Find | Formula | Example |
|---|---|---|
| Voltage | V = I × R | 15A × 8Ω = 120V |
| Current | I = V ÷ R | 120V ÷ 8Ω = 15A |
| Resistance | R = V ÷ I | 120V ÷ 15A = 8Ω |
Voltage Drop Considerations
When electricity travels through wire, some voltage is lost due to wire resistance. The NEC recommends a maximum 3% voltage drop for branch circuits and 5% total from panel to outlet:
- At 120V, 3% = 3.6V drop → outlet delivers ~116.4V (acceptable)
- Long wire runs (over 50 ft) require upsizing the wire gauge to compensate
- Voltage drop = (2 × Length × Current × Wire Resistance) ÷ 1,000