At a standard US residential voltage of 120V, 30 amps is exactly 3,600 watts. If you are running a 240V single-phase circuit (like a dryer or welder receptacle), 30 amps equals 7,200 watts. For a 208V commercial 3-phase system with a typical inductive power factor of 0.8, 30 amps delivers about 8,653 watts. The exact wattage always depends on three fixed assumptions: the system voltage, the number of phases, and the power factor (PF) of the connected load.
The Core Formula and Substituted Values
To convert amps to watts, you cannot use a single universal multiplier. The relationship between current (amps) and real power (watts) is governed by the system's voltage and phase configuration. Here are the foundational formulas with 30 amps substituted into the most common scenarios.
1. DC or Single-Phase AC (Purely Resistive Load)
For DC circuits or AC circuits powering resistive loads (like space heaters or incandescent bulbs) where the power factor is 1.0, the formula is simply:
Watts = Amps × Volts
3,600W = 30A × 120V
2. Single-Phase AC (Inductive Load)
Motors, compressors, and transformers introduce a phase shift between voltage and current. You must multiply by the Power Factor (PF), which typically ranges from 0.7 to 0.9 for industrial equipment:
Watts = Amps × Volts × PF
2,880W = 30A × 120V × 0.80 PF
3. 3-Phase AC (Commercial/Industrial)
In a 3-phase system, you multiply the single-phase result by the square root of 3 (approximately 1.732) to account for the overlapping sine waves:
Watts = Amps × Volts × PF × √3
8,653W = 30A × 208V × 0.80 PF × 1.732
Quick Reference Table: Watts for 24A to 36A
In practical electrical design, you rarely sit at exactly 30 amps. Loads fluctuate, and the National Electrical Code (NEC) requires derating for continuous loads. The table below shows a ±20% range around 30 amps (24A to 36A) across standard voltage configurations. All 3-phase calculations assume a standard commercial 208V supply with a 0.80 power factor.
| Current (Amps) | Watts @ 120V (1Ø, PF 1.0) | Watts @ 240V (1Ø, PF 1.0) | Watts @ 208V (3Ø, PF 0.8) |
|---|---|---|---|
| 24A | 2,880 W | 5,760 W | 6,922 W |
| 27A | 3,240 W | 6,480 W | 7,788 W |
| 30A | 3,600 W | 7,200 W | 8,653 W |
| 33A | 3,960 W | 7,920 W | 9,519 W |
| 36A | 4,320 W | 8,640 W | 10,384 W |
How Voltage, Phase, and Power Factor Shift the Answer
Treating "30 amps" as a fixed wattage is a common trap that leads to tripped breakers or undersized generators. The conversion shifts dramatically based on your regional grid and load type.
120V vs. 230V vs. 240V Systems
In North America, standard residential split-phase power provides 120V for lighting and receptacles, and 240V for heavy appliances. Thus, a 30-amp RV plug (TT-30R) maxes out at 3,600 watts, while a 30-amp dryer receptacle (NEMA 14-30R) can deliver 7,200 watts. However, in the UK, EU, and Australia, standard residential voltage is 230V or 240V single-phase. If you are calculating for a European 230V system, 30 amps yields 6,900 watts, not 7,200. Always verify the nominal voltage printed on the equipment nameplate, as utility tolerances allow a ±5% variance (e.g., 228V to 252V on a 240V nominal system).
The 3-Phase Shift
Commercial facilities use 3-phase power (often 208V or 480V in the US) to run heavy machinery efficiently. Because the three alternating currents peak sequentially, 3-phase systems deliver more continuous power per amp than single-phase. At 480V 3-phase with a 0.85 PF, 30 amps pushes a massive 21,207 watts (21.2 kW).
When the Conversion is Meaningless
If you are dealing with a highly inductive load (like an unloaded transformer or a large HVAC compressor) and you do not know the Power Factor, converting amps directly to watts is electrically meaningless. Without the PF, your calculation only yields Apparent Power, measured in Volt-Amps (VA). Real Power (Watts) is the actual work being done and heat being generated. As detailed in All About Circuits' AC power guide, a motor drawing 30A at 240V with a poor 0.6 PF is only doing 4,320 watts of real mechanical work, despite drawing 7,200 VA of apparent power from the grid.
Frequently Asked Questions
How many watts can a 30-amp breaker handle continuously?
According to NEC Article 210.20(A), a standard thermal-magnetic breaker can only be loaded to 80% of its rating for continuous loads (defined as operating for 3 hours or more). Therefore, a 30-amp breaker is limited to 24 amps of continuous current. At 120V, this means your continuous safe wattage is 2,880 watts. At 240V, it is 5,760 watts. If your load runs continuously, you must size the breaker at 125% of the load, meaning a 30A breaker is the minimum requirement for a 24A continuous load.
How many watts is 30 amps at 12 volts DC?
In automotive, marine, or off-grid solar applications running on a 12V DC battery bank, the formula is simply Watts = Amps × Volts. Therefore, 30 amps at 12V equals exactly 360 watts. This is a critical threshold in vehicle wiring; a 360W load requires at least 10 AWG wire for short runs to prevent excessive voltage drop, and you should protect the circuit with a 30A or 35A ANL fuse located as close to the battery terminal as possible.
Can I plug a 7,200-watt generator into a 30-amp outlet?
Yes, but only if you are using the correct 240V receptacle. A standard NEMA L14-30R twist-lock receptacle is rated for 30 amps at 125/250V. Using the formula (30A × 240V), this outlet can safely handle up to 7,200 watts. However, you cannot split this across 120V legs to pull 7,200W from a standard 120V 30A TT-30 RV plug; that RV plug is strictly limited to 3,600 watts (30A × 120V). Always verify the physical plug configuration and the voltage rating stamped on the generator's alternator housing before connecting a transfer switch.
