Ampere (Amp)
Definition
The ampere (commonly shortened to amp, symbol A) is the SI base unit of electric current, measuring the rate of flow of electric charge through a conductor. One ampere represents approximately 6.24 × 10¹⁸ electrons passing a given point per second. In practical terms: a typical US household outlet provides 15–20 amps, a smartphone charger draws 1–2 amps, a microwave uses 8–12 amps, and an electric dryer requires 24–30 amps. Amps are calculated using Ohm's Law (I = V ÷ R) or the power formula (I = P ÷ V). Circuit breakers are rated in amps to protect wiring from overload.
Why is Ampere (Amp) Important?
In electrical engineering and everyday applications, Ampere (Amp) 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 an Ampere?
The ampere (amp, symbol A) is the SI base unit of electric current — the rate of flow of electric charge through a conductor. Think of amps as the "volume" of electricity flowing, similar to gallons per minute of water through a pipe. Amps are the key measurement for sizing wires, breakers, and electrical panels.
Common Amperage Ratings
| Device/Circuit | Typical Amps | Voltage |
|---|---|---|
| Smartphone charger | 1–2 A | 5V DC |
| Laptop charger | 2–3 A | 19–20V DC |
| Standard outlet (US) | 15–20 A | 120V AC |
| Microwave oven | 8–12 A | 120V AC |
| Window AC unit | 5–15 A | 120V AC |
| Electric dryer | 24–30 A | 240V AC |
| Electric range/oven | 30–50 A | 240V AC |
| EV charger (Level 2) | 30–50 A | 240V AC |
| Main panel (residential) | 100–200 A | 240V AC |
Key Formulas
| Conversion | Formula | Example |
|---|---|---|
| Amps from Watts | A = W ÷ V | 1,500W ÷ 120V = 12.5A |
| Amps from Ohms | A = V ÷ R | 120V ÷ 10Ω = 12A |
| Amps from kVA | A = kVA × 1,000 ÷ V | 5 kVA × 1,000 ÷ 240V = 20.8A |
| Amps from HP | A = HP × 746 ÷ (V × Eff × PF) | 1 HP ÷ (120V × 0.85 × 0.85) ≈ 8.6A |
Wire Sizing by Amperage (NEC)
| Circuit Amps | Minimum Wire Gauge (Copper) | Breaker Size | Typical Use |
|---|---|---|---|
| 15 A | 14 AWG | 15 A | Lighting, bedroom outlets |
| 20 A | 12 AWG | 20 A | Kitchen, bathroom, garage outlets |
| 30 A | 10 AWG | 30 A | Dryer, water heater |
| 40 A | 8 AWG | 40 A | Electric range, cooktop |
| 50 A | 6 AWG | 50 A | Large range, EV charger, sub-panel |