How Many Watts in an Amp?
The number of watts in an amp depends on voltage: at 120 volts (standard US household), 1 amp equals 120 watts. At 240 volts (used for dryers, stoves), 1 amp equals 240 watts. The relationship follows Ohm's Law: Watts = Amps × Volts, meaning amperage alone doesn't determine wattage—you must know the voltage of the circuit.
Understanding the amps-to-watts conversion is essential for calculating circuit capacity (a 15-amp circuit handles 1,800 watts at 120V), determining if you can safely add appliances without overloading breakers, sizing electrical wire for installations, and reading appliance specifications that list only amperage. This knowledge prevents dangerous circuit overloads that cause 28,000 residential fires annually according to the National Fire Protection Association.
This comprehensive guide explains the watts-amps-volts relationship, provides instant conversion calculators for common voltages, breaks down circuit capacity by amp rating, covers real-world appliance examples, explains why voltage matters, and offers practical guidance for safe electrical planning in homes and RVs.
Quick Answer
At 120 Volts (Standard Outlets):
• 1 amp = 120 watts
• 5 amps = 600 watts
• 10 amps = 1,200 watts
• 15 amps = 1,800 watts (standard circuit maximum)
• 20 amps = 2,400 watts (kitchen/bathroom circuits)
At 240 Volts (Major Appliances):
• 1 amp = 240 watts
• 15 amps = 3,600 watts
• 30 amps = 7,200 watts (dryer circuit)
• 50 amps = 12,000 watts (range circuit)
Key Formula: Watts = Amps × Volts
⚡ Multi-Function Electrical Calculator
Convert Amps to Watts
Convert Watts to Amps
Circuit Capacity Calculator
Understanding the Watts-Amps-Volts Relationship
Watts, amps, and volts are interconnected through Ohm's Law. You cannot convert amps to watts without knowing voltage.
The Core Formula
Why Voltage Matters: The same 15 amps carries different power at different voltages. This is why major appliances use 240V—they can deliver more power without requiring thicker wires for higher amperage.
Common Amp-to-Watt Conversions
At 120 Volts (Standard US Outlets)
| Amps | Watts | Typical Appliances | Circuit Type |
|---|---|---|---|
| 1 A | 120 W | LED bulbs, phone chargers | Any circuit |
| 3 A | 360 W | Laptop, small TV | Any circuit |
| 5 A | 600 W | Coffee maker, toaster | 15A circuit |
| 8 A | 960 W | Hair dryer, vacuum | 15A circuit |
| 10 A | 1,200 W | Window AC, iron | 15A dedicated |
| 12.5 A | 1,500 W | Space heater (max) | 15A dedicated |
| 15 A | 1,800 W | Circuit maximum | 15A breaker |
| 20 A | 2,400 W | Circuit maximum | 20A breaker |
At 240 Volts (Major Appliances)
| Amps | Watts | Typical Appliances | Circuit Type |
|---|---|---|---|
| 10 A | 2,400 W | Small window AC (240V) | 15A @ 240V |
| 15 A | 3,600 W | Electric dryer (small) | 20-30A @ 240V |
| 20 A | 4,800 W | Electric water heater | 30A @ 240V |
| 25 A | 6,000 W | Central AC unit | 30-40A @ 240V |
| 30 A | 7,200 W | Electric dryer (standard) | 30A @ 240V |
| 40 A | 9,600 W | Electric range/oven | 40-50A @ 240V |
| 50 A | 12,000 W | Large electric range | 50A @ 240V |
Circuit Capacity by Breaker Size
Understanding circuit capacity prevents overloads and electrical fires.
| Breaker | Max Watts | Safe Continuous | Typical Rooms |
|---|---|---|---|
| 15A @ 120V | 1,800 W | 1,440 W (80%) | Bedrooms, living rooms |
| 20A @ 120V | 2,400 W | 1,920 W (80%) | Kitchen, bathroom, garage |
| 30A @ 240V | 7,200 W | 5,760 W (80%) | Electric dryer |
| 40A @ 240V | 9,600 W | 7,680 W (80%) | Electric range |
| 50A @ 240V | 12,000 W | 9,600 W (80%) | Large range, RV hookup |
⚠️ 80% Rule: NEC (National Electrical Code) requires continuous loads (running 3+ hours) stay at or below 80% of circuit capacity. A 15A circuit's safe continuous load is 1,440W, not 1,800W.
Why Different Voltages Exist
120V Circuits: Standard outlets for most household items. Lower voltage = safer for routine use.
240V Circuits: Major appliances requiring high power. Benefits:
- Lower Amperage: 3,600W at 240V = 15A vs 30A at 120V
- Thinner Wire: Lower amps allow smaller gauge wire (cheaper, easier installation)
- Less Voltage Drop: More efficient over long wire runs
- Smaller Breakers: 240V circuits handle more power with same amp rating
Real-World Examples
Example 1: Can I Add a Space Heater?
Situation: 15A bedroom circuit already has TV (150W), lamp (60W), laptop (65W)
Example 2: Sizing a Generator
Goal: Run refrigerator (800W), TV (120W), lights (100W), laptop charger (65W)
Low Voltage Systems (12V/24V)
RVs, boats, and solar systems use 12V or 24V DC power with very different amp requirements.
12V System Conversions
| Watts | Amps @ 12V | Amps @ 120V | Why It Matters |
|---|---|---|---|
| 120 W | 10 A | 1 A | RV lighting draws 10× more amps than AC equivalent |
| 600 W | 50 A | 5 A | Microwave requires massive 12V wiring |
| 1,200 W | 100 A | 10 A | Hair dryer would drain RV battery instantly |
Key Insight: Low voltage = high amperage for same power. This is why RVs convert 12V DC to 120V AC for high-wattage appliances.
Frequently Asked Questions
How many watts can a 15-amp circuit handle?
1,800 watts maximum (15A × 120V), but only 1,440 watts for continuous loads per NEC 80% rule. Continuous means running 3+ hours like a space heater or refrigerator. Brief loads like microwaves or hair dryers can use up to 1,800W.
Why do I need to know volts to convert amps to watts?
Because amps measure current flow while watts measure power consumption. The same amperage delivers different power at different voltages: 10 amps at 120V = 1,200W, but 10 amps at 240V = 2,400W. Voltage is the "pressure" pushing the current, so you need both values to calculate power.
How many amps is 1500 watts at 120V?
12.5 amps (1,500W ÷ 120V = 12.5A). This is 83% of a 15-amp circuit's capacity, which is why 1,500W is the standard maximum for portable heaters—it's the highest wattage that fits safely on standard 15A household circuits.
Can I use a 20-amp appliance on a 15-amp circuit?
No. A 20-amp appliance draws 2,400W at 120V, which exceeds the 15-amp circuit's 1,800W capacity. The breaker will trip immediately. You need a dedicated 20-amp circuit. Never use adapters to force 20A plugs into 15A outlets—this creates fire hazards.
Conclusion
The number of watts in an amp depends entirely on voltage: at 120V (standard US outlets), 1 amp equals 120 watts, while at 240V (major appliances), 1 amp equals 240 watts. The fundamental relationship Watts = Amps × Volts means you cannot convert between amps and watts without knowing the voltage of the circuit or appliance.
For household electrical planning, the most critical conversion is understanding that a standard 15-amp, 120-volt circuit provides 1,800 watts maximum capacity, but the NEC 80% rule limits continuous loads (3+ hours operation) to 1,440 watts for safety. This explains why space heaters max out at 1,500 watts—12.5 amps at 120V fits within safe continuous use limits.
Higher voltage circuits like 240V deliver more power at the same amperage: a 30-amp circuit at 240V provides 7,200 watts versus just 3,600 watts at 120V. This is why electric dryers, ranges, and water heaters use 240V—they can deliver high power without requiring impractically thick wiring to handle the high amperage that would be needed at 120V.
For practical applications: calculate total amperage before adding appliances to circuits (divide watts by voltage), stay under 80% of circuit capacity for safety, and remember that low-voltage systems (12V RV/solar) require 10× higher amperage than 120V systems for the same wattage, necessitating much thicker wiring despite lower voltage.
Data sources: U.S. Department of Energy (DOE), National Electrical Code (NEC), and National Fire Protection Association (NFPA). Electrical standards based on 2026 code requirements.