There is no fixed number of amps in 240 volts because volts measure electrical pressure while amps measure current flow. However, if you are asking how many amps a specific 240V appliance draws, the answer depends entirely on its wattage. For a standard baseline—a 4,800-watt 240V electric water heater—the draw is exactly 20 amps. The formula used with substituted values is: 4,800W ÷ 240V = 20A. Volts and amps are fundamentally different dimensions; you can only bridge them by introducing power (watts) or resistance (ohms) into the equation.
The Core Formula and Baseline Assumptions
To calculate amperage on a 240V circuit, you must use Watt’s Law. For direct current (DC) or single-phase alternating current (AC) with a purely resistive load, the formula is:
I = P ÷ V
(Current in Amps = Power in Watts ÷ Voltage in Volts)
The 20A answer for a 4,800W load assumes a single-phase, purely resistive load with a Power Factor (PF) of exactly 1.0. Heating elements and incandescent bulbs are resistive. If your load is inductive (like an air conditioner compressor or a well pump motor), the magnetic fields cause the current and voltage waveforms to fall out of sync.
According to the Fluke Power Quality Guide, inductive loads require you to factor in the Power Factor (PF). The modified AC formula becomes I = P ÷ (V × PF). If a 240V motor draws 4,800W of real power but has a PF of 0.8, it actually pulls 25 amps from the panel (4800 ÷ [240 × 0.8] = 25A), not 20.
When the Conversion is Meaningless: If you are sizing wire for an inductive load and you do not know the manufacturer’s stated Power Factor or the phase angle, calculating amps from real power (Watts) is mathematically meaningless. You must use the nameplate Apparent Power (VA) or measure the running current directly with a true-RMS clamp meter.
Neighboring Values: 240V Amperage Chart (±20% Range)
Most residential 240V heavy appliances (water heaters, baseboard heaters, dryers) cluster around the 4,800W mark. Below is a reference chart showing how the amperage shifts across a ±20% wattage range. This is critical for verifying if an existing 20A or 30A breaker can handle a replacement appliance.
| Appliance Wattage (W) | Voltage (V) | Calculated Amps (A) | Minimum Breaker Size (Continuous) |
|---|---|---|---|
| 3,840W (-20%) | 240V | 16.0A | 20A |
| 4,200W (-12.5%) | 240V | 17.5A | 25A |
| 4,800W (Baseline) | 240V | 20.0A | 30A |
| 5,200W (+8.3%) | 240V | 21.6A | 30A |
| 5,760W (+20%) | 240V | 24.0A | 35A |
Note: Breaker sizes assume the load runs for 3 hours or more (continuous), requiring the NEC 125% safety multiplier. A 20A continuous load requires a 25A breaker minimum, but 30A is the standard commercial off-the-shelf size.
How the Math Shifts Across Global Voltages
The 240V standard is common in North America for split-phase heavy appliances, but nominal voltages shift depending on your region and phase configuration. As All About Circuits outlines in their DC and AC power primers, keeping wattage constant while dropping voltage forces amperage upward. Here is how a 4,800W load behaves across different systems:
- 120V (US Standard Branch Circuit): 4,800W ÷ 120V = 40 Amps. This is why high-wattage appliances do not use standard 120V wall outlets; the current would melt 14 AWG wire and instantly trip a 15A or 20A breaker.
- 230V (EU/UK/AU Nominal Mains): 4,800W ÷ 230V = 20.8 Amps. European single-phase systems operate at 230V nominal. The amperage is slightly higher than the US 240V equivalent, requiring marginally thicker wire or a 25A/32A MCB (Miniature Circuit Breaker).
- 208V (US Commercial 3-Phase Wye): 4,800W ÷ (208V × √3) = 13.3 Amps per leg. In commercial buildings, 3-phase power distributes the load across three hot wires, drastically reducing the amperage burden on any single conductor.
Decision Path: Sizing Breakers and Wire for 240V Loads
Use this decision tree to select the correct breaker and copper wire gauge for your 240V project. This path assumes standard 60°C to 75°C terminal ratings and copper THHN or NM-B conductors in a standard 30°C ambient environment.
| IF Your 240V Load Is... | AND the Max Continuous Draw Is... | THEN Pick This Breaker | AND This Copper Wire (AWG) |
|---|---|---|---|
| Small Baseboard Heater | ≤ 12A (2,880W) | 15A Double-Pole | 14 AWG NM-B |
| Standard Water Heater | ≤ 20A (4,800W) | 30A Double-Pole | 10 AWG THHN / 10/2 NM-B |
| Electric Dryer / Range | ≤ 30A (7,200W) | 40A Double-Pole | 8 AWG THHN / 8/3 NM-B |
| Level 2 EV Charger | 48A Continuous (11.5kW) | 60A Double-Pole | 6 AWG THHN in conduit |
If you are installing a modern 48A continuous Level 2 EV charger (like the ChargePoint Home Flex or Tesla Wall Connector) on a 240V circuit, the NEC 125% continuous load rule dictates a 60A breaker. Terminate your run using 6 AWG copper THHN wire pulled through 3/4-inch EMT conduit. Do not use 6 AWG NM-B (Romex) for a 60A breaker, as NM-B is strictly limited to the 60°C ampacity column (55A), which violates code for a 60A overcurrent device.
Frequently Asked Questions
Can I use a 20A breaker for a 4,800W 240V water heater?
No. While 4,800W ÷ 240V equals exactly 20A, a water heater is classified as a continuous load. NEC-style guidance requires continuous loads to be derated to 80% of the breaker’s capacity. 80% of a 20A breaker is 16A. Therefore, a 20A load will eventually cause a 20A breaker to trip from thermal fatigue. You must step up to a 25A or 30A breaker.
Why does my multimeter read 245V instead of 240V?
Nominal voltage is just a label. Utility transformers are designed to deliver slightly higher voltage at the panel to account for voltage drop under load. A reading between 235V and 248V is entirely normal and will slightly reduce your amperage draw (e.g., 4,800W ÷ 245V = 19.5A).
Does 240V use less electricity than 120V?
No. Your utility company bills you for Watt-hours (energy), not amps. Running a 4,800W heater on 240V draws 20A, while running the exact same 4,800W heating element on 120V would draw 40A. The energy consumed and the cost to run it are identical; the 240V system simply uses thinner, cheaper wire to deliver the same power.
