Converting 30 amperes to watts requires a fixed voltage, because amperes measure current flow while watts measure total power delivery. At a standard US 120V single-phase supply, 30 amps equals exactly 3,600 watts. At a European or UK 230V single-phase supply, 30 amps equals 6,900 watts. For a commercial 208V 3-phase system, 30 amps yields 10,808 watts.
• 120V AC/DC: 3,600 W
• 230V AC: 6,900 W
• 208V 3-Phase: 10,808 W
• 480V 3-Phase: 24,941 W
The Core Formula and the Assumptions That Fix Your Answer
You cannot convert amps to watts without making three critical assumptions: voltage, phase (single vs. three-phase), and power factor (PF). If any of these are missing, the calculation is incomplete.
For direct current (DC) or single-phase alternating current (AC) with a purely resistive load (like a space heater or incandescent bulb), the formula is straightforward:
Watts = Amps × Volts × Power Factor
Substituting our target values for a 120V resistive circuit (where PF = 1.0):
3,600 W = 30 A × 120 V × 1.0
For 3-phase AC power, the formula introduces the square root of 3 (approximately 1.732) to account for the phase angle offsets:
Watts = Amps × Volts × Power Factor × 1.732
How 30 Amps Shifts Across 120V, 230V, and 3-Phase Systems
The physical current (30A) remains the same, but the total work done (watts) scales with the electrical pressure (voltage) and the number of phases. Here is how a 30-amp draw translates across common global and industrial systems, assuming a unity power factor (1.0).
| System Type | Nominal Voltage | Phase | Calculated Watts (PF=1.0) | Common Application |
|---|---|---|---|---|
| US Standard Receptacle | 120V | Single | 3,600 W | RV TT-30 plug, heavy duty tools |
| US Dryer/Range Circuit | 240V | Single (Split) | 7,200 W | EV chargers, welders, dryers |
| EU / UK Standard | 230V | Single | 6,900 W | EU induction hobs, EV chargers |
| US Commercial Light | 208V | 3-Phase | 10,808 W | HVAC units, commercial lighting |
| US Industrial Heavy | 480V | 3-Phase | 24,941 W | Large motors, manufacturing |
Neighboring Ampacity Values (24A to 36A) at 120V
When sizing wires and breakers, you rarely operate at the exact theoretical maximum. The National Electrical Code (NEC) requires continuous loads (those running for 3 hours or more) to be derated to 80% of the breaker's rating. For a 30-amp breaker, your continuous safe limit is 24 amps.
Here is a ±20% range table for 120V single-phase systems to help you size your loads safely:
| Current (Amps) | Watts at 120V (PF=1.0) | NEC 80% Rule Context |
|---|---|---|
| 24 A | 2,880 W | Maximum continuous load on a 30A breaker |
| 27 A | 3,240 W | Non-continuous peak (e.g., motor startup) |
| 30 A | 3,600 W | Absolute breaker trip threshold |
| 33 A | 3,960 W | Will trip a 30A breaker instantly |
| 36 A | 4,320 W | Requires a 40A or 50A breaker upgrade |
When Converting 30 Amperes to Watts is Meaningless
If you are measuring an inductive or capacitive load—such as an AC motor, a transformer, or a fluorescent lighting ballast—and you do not know the Power Factor (PF), converting 30 amps to watts using the basic formula will give you the apparent power (Volt-Amps, or VA), not the real power (Watts).
For example, if a 3-phase motor draws 30 amps at 208V, the apparent power is 10,808 VA. But if the motor's power factor is 0.75, the actual real power doing mechanical work is only 8,106 watts. The remaining 2,702 VA is reactive power bouncing back and forth in the magnetic fields. Always check the equipment nameplate for the PF rating or use a true-RMS power meter to measure real watts directly.
Frequently Asked Questions
How many watts can a 30-amp breaker handle continuously?
Under NEC Article 210.20, a 30-amp breaker can handle a maximum continuous load of 24 amps (80% of the rating). On a standard 120V circuit, this equals 2,880 watts. On a 240V circuit (like a double-pole breaker), the continuous limit is 5,760 watts. If your load runs for less than 3 hours at a time, you can safely pull the full 3,600W (120V) or 7,200W (240V).
What size generator do I need for a 30-amp RV plug?
A standard 30-amp RV plug (NEMA TT-30) operates at 120V single-phase. The absolute maximum draw is 3,600 watts. However, to account for the starting surge of RV air conditioners and to keep the generator from running at 100% capacity (which causes voltage sag and harmonic distortion), you should use a generator rated for at least 4,000 to 4,500 running watts.
Why does my 30-amp EV charger not pull 7,200 watts?
If you installed a 30-amp double-pole breaker (240V) for an EV charger, the NEC 80% continuous load rule limits the actual charging current to 24 amps. Therefore, 24 amps × 240 volts equals 5,760 watts (or 5.76 kW), not 7,200 watts. To achieve a true 7.2 kW (30A) charge rate, you must install a 40-amp breaker and use 8 AWG copper wire.
