There is no single fixed answer to "how many amps is 240 volts" because voltage (electrical pressure) and amperage (electrical current) measure fundamentally different properties. However, if you need a direct baseline: a 2,400-watt resistive load connected to a 240-volt single-phase circuit draws exactly 10 amps. If you are running a 4,800-watt electric water heater on that same 240V circuit, it draws 20 amps.
To find the exact amperage for your specific setup, you must know the wattage of the load. The core formula with values substituted looks like this:
Amps = Watts ÷ Volts
10A = 2,400W ÷ 240V
The Core Formula and Assumptions That Fix the Answer
The conversion from volts to amps is entirely dependent on three fixing assumptions: Wattage (Real Power), Power Factor (PF), and Phase Count. If you only know the voltage is 240V, the conversion is mathematically impossible.
For standard resistive loads—like electric baseboard heaters, toaster ovens, or incandescent lighting—the Power Factor is 1.0. The simple DC-style formula (I = P / V) works perfectly here. But the moment you introduce inductive loads like HVAC compressors, well pumps, or large motors, the conversion becomes meaningless if the Power Factor is unknown.
Motors and transformers require reactive power to create magnetic fields. If a 240V motor nameplate lists 2,400W of real power but has a Power Factor of 0.80, the actual current draw is I = 2400 / (240 × 0.80) = 12.5 amps, not 10 amps. Sizing a breaker based on the 10A calculation will result in nuisance tripping or melted wire insulation. Always use the Full Load Amps (FLA) printed on the motor nameplate for inductive loads, as recommended by the NFPA 70 National Electrical Code (NEC).
Quick Reference Chart: 240V Amp Draw (±20% Load Range)
The table below maps out the amperage for a baseline 4,800-watt load (a common size for heavy-duty shop heaters or large water heaters) across a ±20% wattage range. This is critical for understanding how slight variations in actual appliance wattage affect your branch circuit sizing.
| Load Variance | Wattage (W) | Amps at 240V | Minimum Copper Wire (THHN) |
|---|---|---|---|
| -20% | 3,840W | 16.0A | 12 AWG |
| -10% | 4,320W | 18.0A | 12 AWG |
| Baseline | 4,800W | 20.0A | 12 AWG |
| +10% | 5,280W | 22.0A | 10 AWG |
| +20% | 5,760W | 24.0A | 10 AWG |
Note: Wire sizing assumes 75°C termination ratings and standard residential ambient temperatures. If the load runs for 3 hours or more (continuous load), NEC Article 210.20 requires you to multiply the amp draw by 1.25 for breaker sizing.
How the Math Shifts: 120V, 230V, and 3-Phase Systems
Treating 240V as a universal constant is a common mistake that leads to undersized breakers and voltage drop issues. Here is how the amperage shifts when the electrical environment changes.
The 120V Shift (North American Standard Branch)
If you take that same 4,800W load and attempt to run it on a standard 120V household outlet, the amperage doubles to 40 amps (4800W / 120V). This is exactly why heavy appliances use 240V: doubling the voltage halves the current, allowing you to use smaller, cheaper wire (12 AWG instead of 8 AWG) and minimizing voltage drop over long wire runs.
The 230V Shift (European / UK / AU Nominal)
Many international appliances are rated for 230V nominal, even if colloquially called "240V". If you plug a strict 4,800W resistive heater designed for 240V into a true 230V supply, it will actually draw slightly less current (20.87A), but it will only output about 4,420W of heat. Conversely, if the appliance actively regulates its power draw to maintain exactly 4,800W at 230V, the current increases to 20.87A, which could push a borderline 20A breaker into thermal trip territory over time.
The 3-Phase Shift (Industrial / Commercial)
For 240V 3-phase power, the formula introduces the square root of 3 (1.732). Assuming a motor with a 0.85 Power Factor drawing 4,800W of real power:
Amps = 4800 / (240 × 1.732 × 0.85) = 13.56 Amps
Three-phase systems deliver power more efficiently, resulting in a significantly lower amp draw per leg compared to single-phase systems for the same real power output.
Frequently Asked Questions
How many amps is 240 volts on a 50 amp breaker?
A 240V circuit protected by a 50-amp breaker can safely deliver up to 50 amps of peak current, which equates to a maximum of 12,000 watts (240V × 50A). However, if the load is continuous (running for 3 hours or more, like an EV charger or kiln), the NEC 80% rule limits the continuous draw to 40 amps (9,600 watts). The breaker itself does not dictate the amps; it only sets the absolute ceiling before the thermal-magnetic trip mechanism engages to protect the wire.
How many amps does a 240V electric baseboard heater draw?
It depends entirely on the physical length and wattage rating of the heater. A standard 6-foot, 1,500-watt 240V baseboard heater draws 6.25 amps. A larger 8-foot, 2,000-watt model draws 8.33 amps. Because these are considered continuous loads, you must multiply the amp draw by 1.25 for circuit sizing. Therefore, the 2,000W heater requires a circuit sized for at least 10.4 amps, meaning a standard 15-amp double-pole breaker and 14 AWG wire is the legal minimum, though 12 AWG on a 20-amp breaker is the preferred best practice for voltage drop mitigation.
Why does my 240V well pump draw more amps on startup?
Inductive motors require a massive surge of current to overcome initial inertia and establish the magnetic field in the stator windings. This is known as Locked Rotor Amperage (LRA). A 240V well pump that draws a steady 10 amps while running (Full Load Amps) might spike to 50 or 60 amps for the first half-second of startup. This is normal. Your breaker must be sized to tolerate this momentary inrush current without tripping, which is why motor circuits often use specific time-delay breakers or motor-rated disconnects as outlined in NEC Article 430.
What happens to the amp draw if my 240V supply drops to 220V?
For purely resistive loads (like space heaters or incandescent lights), a voltage drop to 220V will actually decrease the amp draw and significantly reduce the total wattage output. The heater will simply run cooler. However, for inductive motor loads (like an AC compressor or table saw), the motor will attempt to maintain its mechanical power output by increasing its amp draw to compensate for the lower voltage. This elevated current generates excess heat in the windings, which is why chronic low-voltage conditions at the end of long feeder lines can burn out 240V motors prematurely. Always verify your supply voltage with a true-RMS multimeter under load.
