At a standard US residential voltage of 120V, 30 amps is exactly 3,600 watts. If you are running a 240V circuit (like a dryer or RV hookup), 30 amps equals 7,200 watts. For a 208V 3-phase commercial system, 30 amps delivers roughly 10,817 watts. The foundational formula used here is Watts = Amps × Volts (W = I × V). Substituting our exact query values for a standard 120V branch circuit: 3,600W = 30A × 120V.
However, treating a single voltage as a universal answer is a common trap. The true wattage depends entirely on the system voltage, the number of phases, and the power factor of the load. Below is the complete breakdown of how this conversion shifts across different electrical environments.
The Core Formula and the Assumptions That Fix the Answer
To convert amps to watts accurately, three specific assumptions must be locked in. If any of these variables change, your final wattage changes with them.
- Voltage (V): Are you measuring a 120V standard outlet, a 240V split-phase appliance circuit, or a 230V European mains supply? Voltage is the electrical pressure pushing the current.
- Phase: Single-phase power (standard residential) uses a simple multiplication formula. Three-phase power (commercial/industrial) requires multiplying by the square root of 3 (approximately 1.732) to account for the overlapping AC waveforms.
- Power Factor (PF): This is the ratio of real power (Watts) to apparent power (Volt-Amps). For purely resistive loads like space heaters or incandescent bulbs, PF is 1.0. For inductive loads like motors or compressors, PF drops (often to 0.8 or 0.9), meaning the actual wattage is lower than the raw V × A calculation.
The universal AC power formula incorporating all three assumptions is:
Watts = Amps × Volts × Power Factor × Phase Multiplier
Quick-Reference Conversion Table (±20% Range)
When sizing breakers or wiring, you rarely deal with exactly 30.0 amps on the dot. Loads fluctuate. Here is a spec-sheet-table showing the wattage for a ±20% range around 30 amps (24A to 36A) across the three most common supply voltages. The 3-phase column assumes a standard 208V commercial supply with a conservative 0.90 Power Factor.
| Current (Amps) | 120V Single-Phase (PF=1.0) | 240V Single-Phase (PF=1.0) | 208V 3-Phase (PF=0.9) |
|---|---|---|---|
| 24A (-20%) | 2,880 W | 5,760 W | 7,780 W |
| 27A (-10%) | 3,240 W | 6,480 W | 8,752 W |
| 30A (Base) | 3,600 W | 7,200 W | 9,724 W |
| 33A (+10%) | 3,960 W | 7,920 W | 10,697 W |
| 36A (+20%) | 4,320 W | 8,640 W | 11,669 W |
How the Math Shifts: 120V vs 230V vs 3-Phase Systems
Let us look at how the exact same 30-amp current draw translates to real-world work (watts) depending on where you plug it in.
Standard 120V US Branch Circuits
In North America, standard wall outlets are 120V nominal. A 30-amp draw here yields 3,600 watts. This is typical for a dedicated 30A circuit powering a large window AC unit, an RV pedestal, or a heavy-duty commercial vacuum. The math is straightforward: 30A × 120V × 1.0 PF = 3,600W.
230V / 240V Split-Phase and European Mains
If you are in Europe or running a 240V appliance in the US (like a welder or kiln), the voltage doubles. Therefore, the wattage doubles. At 240V, 30 amps equals 7,200 watts. At the European harmonized standard of 230V, 30 amps equals 6,900 watts. This is why a 30A 240V circuit can run a massive electric heater that would instantly trip a 120V breaker.
208V and 400V Three-Phase Systems
In commercial settings, 3-phase power is standard. The formula shifts to include the square root of 3 (1.732). For a 208V 3-phase system at a 0.95 power factor, the calculation is: 30A × 208V × 1.732 × 0.95 = 10,265 watts. In a 400V 3-phase European industrial system, that same 30A draw pushes nearly 19,744 watts. According to the All About Circuits AC power guide, the phase multiplier accounts for the fact that three overlapping waveforms deliver power more continuously than a single wave.
When the Amp-to-Watt Conversion Becomes Meaningless
There is one major scenario where converting 30 amps to watts without extra data is useless: when the Power Factor (PF) is unknown on a highly reactive load.
If you clamp a multimeter around a wire feeding a large 3-phase induction motor and read 30 amps, you are measuring apparent current. If the motor has a poor power factor of 0.6 (common in lightly loaded, older motors), the actual real power (Watts) doing useful work is 40% lower than the V × A calculation suggests. The remaining energy is simply bouncing back and forth as reactive power (VARs).
Frequently Asked Questions
How many watts can a 30-amp breaker safely handle continuously?
Under NEC guidelines, a breaker can only be loaded to 80% of its rating for continuous loads (those running for 3 hours or more). Therefore, a 30-amp breaker is limited to 24 continuous amps. At 120V, this means your safe continuous wattage is 2,880 watts. At 240V, it is 5,760 watts. You can pull the full 3,600W (at 120V) for non-continuous, short-duration loads.
Is 30 amps enough to power a standard travel trailer RV?
Yes. A standard 30-amp RV service is a 120V single-phase system. This provides a maximum of 3,600 watts. This is generally enough to run one 15,000 BTU roof AC unit (approx. 1,500W - 1,800W), a microwave (1,000W), and a few LED lights and a TV simultaneously, provided you do not turn on the electric water heater element at the same time.
How many watts is 30 amps in a 12V DC automotive or solar system?
In DC systems, there is no power factor or phase to worry about. The formula is strictly W = V × A. Therefore, 30 amps at 12V DC equals exactly 360 watts. If you are wiring a 300W solar inverter or a heavy-duty winch to a 12V battery bank, you will need wire rated for at least 30A (typically 10 AWG copper for short runs in engine bays).
What size wire do I need to safely carry 30 amps?
Wire sizing depends on the insulation type and installation method. For standard NM-B (Romex) cable run through residential walls, you must use 10 AWG copper, which is rated for 30A on the 60°C column of the NEC ampacity table. If you are pulling individual THHN wires through conduit, 10 AWG is still standard, though its 75°C rating technically allows higher ampacity; the breaker termination limits usually cap it at the 60°C rating anyway. Never use 12 AWG or 14 AWG on a 30A breaker, as this creates a severe fire hazard.
