At 120V (standard US household voltage), 30 amps equals exactly 3,600 watts. At 240V (US heavy appliance voltage), 30 amps equals 7,200 watts. In a 208V 3-phase commercial system, 30 amps delivers roughly 10,810 watts. You cannot answer how many watts are in 30 amps with a single universal number because watts measure real power consumption, while amps measure the volume of current flow. The exact conversion is entirely fixed by three assumptions: system voltage, phase configuration, and power factor.
The Core Formula and Substituted Values
To convert amperage to wattage, you must multiply the current by the electrical pressure (voltage). For direct current (DC) or single-phase alternating current (AC) with a purely resistive load (like a heating element or incandescent bulb), the power factor is 1.0, simplifying the math.
Substituted for 120V: 3,600W = 30A × 120V
Substituted for 240V: 7,200W = 30A × 240V
For 3-phase AC power, commonly found in commercial panels and industrial machinery, the formula introduces a multiplier for the phase angle difference (the square root of 3, or roughly 1.732) and the power factor (PF).
Substituted for 208V (PF 1.0): 10,810W = 30A × 208V × 1.732 × 1.0
Neighboring Amp-to-Watt Conversion Table (24A–36A)
Circuit loads rarely sit at a perfect, static 30.0 amps. Motors surge on startup, and resistive heaters fluctuate with ambient temperature. The table below maps a ±20% range around 30 amps across the three most common North American and European voltage standards, assuming a 1.0 power factor.
| Current (Amps) | 120V Single-Phase (Watts) | 230V/240V Single-Phase (Watts) | 208V 3-Phase (Watts) |
|---|---|---|---|
| 24A (-20%) | 2,880W | 5,520W / 5,760W | 8,648W |
| 27A (-10%) | 3,240W | 6,210W / 6,480W | 9,729W |
| 30A (Baseline) | 3,600W | 6,900W / 7,200W | 10,810W |
| 33A (+10%) | 3,960W | 7,590W / 7,920W | 11,891W |
| 36A (+20%) | 4,320W | 8,280W / 8,640W | 12,972W |
How Voltage, Phase, and Power Factor Shift the Result
If you only memorize one number, you will make a dangerous sizing error. The conversion from amps to watts shifts dramatically based on the physical reality of the circuit you are measuring.
120V vs. 230V vs. 240V Shifts
In North America, standard receptacles are 120V, meaning a 30-amp RV plug or a 30-amp breaker feeding a standard outlet maxes out at 3,600 watts. However, large appliances (dryers, welders, EV chargers) use split-phase 240V, doubling the wattage to 7,200 watts for the exact same 30-amp current limit. In Europe and the UK, the standard single-phase voltage is 230V. Therefore, a 30-amp draw on a UK ring main or European industrial socket yields 6,900 watts. The current (amps) is identical; the work done (watts) changes because the electrical pressure (volts) is higher.
The 3-Phase Multiplier
Commercial buildings use 3-phase power (often 208V or 400V) to run heavy HVAC and machinery. Because the three sine waves overlap, 3-phase systems deliver power more continuously. This is why the √3 (1.732) multiplier exists in the formula. A 30-amp draw on a 208V 3-phase system yields over 10.8 kilowatts—three times the power of a 120V single-phase circuit at the same amperage.
When the Conversion is Meaningless: Unknown Power Factor
The formulas above assume a Power Factor (PF) of 1.0, which is only true for purely resistive loads like water heaters or toaster ovens. According to Fluke’s electrical engineering guides, inductive loads like AC compressors, blower motors, and transformers create a phase shift between voltage and current. This results in a PF of roughly 0.8 to 0.9. If you are measuring 30 amps on an inductive motor circuit and do not know the exact power factor, calculating real watts is mathematically meaningless. You can only calculate Apparent Power (Volt-Amps, or VA). Real Watts will always be lower than VA on inductive circuits.
Frequently Asked Questions
How many watts can a 30-amp breaker safely handle continuously?
Under National Electrical Code (NEC) Article 210.20, a 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 draw. At 120V, your safe continuous wattage limit is 2,880 watts. At 240V, it is 5,760 watts. Non-continuous, intermittent loads can use the full 3,600W / 7,200W capacity.
What wire size is required for a 30-amp circuit?
For standard copper conductors in residential and commercial wiring, you must use a minimum of 10 AWG copper wire. This applies to both THHN in conduit and NM-B (Romex) cable. Never use 12 AWG (rated for 20A) or 14 AWG (rated for 15A) on a 30-amp breaker, as the wire will overheat and melt before the breaker trips, creating a severe fire hazard. If you are running aluminum wire, you must step up to 8 AWG.
Is 30 amps enough to run an RV or camper?
Yes, a standard 30-amp RV service is a 120V single-phase circuit, providing a maximum of 3,600 watts. This is generally sufficient to run one 15,000 BTU roof air conditioner (which draws roughly 1,500 to 1,800 watts) alongside a microwave, a television, and LED lighting. However, it is not enough to run two roof AC units simultaneously while using high-draw appliances like a coffee maker or an electric space heater, which will quickly push the draw past 30 amps and trip the pedestal breaker.
Why does a 3,600W motor draw more than 30 amps at 120V?
If you look at the nameplate of a 120V motor rated for 3,600 watts (roughly 4.8 horsepower), you will notice the Full Load Amps (FLA) rating is often well over 35 or 40 amps, not 30 amps. This happens for two reasons: power factor and motor efficiency. The 3,600W rating is the mechanical output power at the shaft, not the electrical input power. When you account for a typical 85% motor efficiency and a 0.85 power factor, the electrical input required to produce that mechanical work is much higher, forcing the motor to draw significantly more current than a simple 3,600W ÷ 120V calculation would suggest.
