Hello! In the previous lesson, you read appliance labels to identify their supply requirements and power ratings. Now you can put one of those ratings to work: given the wattage of a resistive household appliance, you will estimate how much current it draws from Turkey’s nominal 230 V AC supply.
Allow about 35–40 minutes, including the short video, reading, and worked examples. This is a calculation from a label, not a measurement: you do not need to plug anything in, open equipment, or use a meter on a household outlet.
From watts to amps
Power describes how quickly an appliance uses electrical energy; its unit is the watt (W). Current describes the flow of electric charge; its unit is the ampere (A), usually shortened to amp. For a resistive appliance operating at its rated voltage, power, voltage, and current are related by
Here is power in watts, is voltage in volts, and is current in amps. To find current when you know power and voltage, divide:
Watch this short explanation of the relationship. Its examples use solar equipment and other voltages; we will apply the same calculation to a resistive appliance on a 230 V AC supply.
Electricity Explained: Volts, Amps, Watts, Fuse Sizing, Wire Gauge, AC/DC, Solar Power and more!
Watch “Electricity Explained: Volts, Amps, Watts, Fuse Sizing, Wire Gauge, AC/DC, Solar Power and more!” from DIY Solar Power with Will Prowse for the power calculation and its rearrangement.
Watch watts and amps for how voltage and current combine to give power. Continue through finding current, where the presenter divides watts by volts when an appliance label does not state amps.
For household calculations, use 230 V unless a question specifies another voltage. The supply is AC, but 230 V is its nominal RMS voltage—the voltage figure used with the appliance’s rated power in this calculation. You do not need to work with the changing AC waveform to make this estimate.
A useful mental check is that, at 230 V, approximately 230 W corresponds to 1 A for a resistive load operating at that power. An appliance rated in the thousands of watts will therefore draw several amps, not a few milliamps.
Calculate from an appliance label
Suppose an electric heater is marked 230 V ~ 50 Hz, 2000 W. The previous lesson established that these are its AC input ratings. Using its power rating:
So, while the heater is operating at about 2000 W, its estimated current is 8.7 A. Notice the units: watts divided by volts gives amps.
If a label uses kilowatts (kW), convert to watts first. For a resistive appliance rated 1.5 kW:
The image below makes the same calculation for a 100 W lamp. Concentrate on the 230 V case, which gives about 0.435 A, or 435 mA. The 120 V case shows why you must use the voltage that belongs to the appliance’s rating; it does not mean that a particular 120 V bulb can safely be used at 230 V. The high voltages shown on the transformer diagrams are not needed for this lesson’s calculation.
What makes the answer an estimate?
The calculation is most direct for a mainly resistive load, such as a basic heating element. Electrical power is converted chiefly into heat. A lamp with a filament can also serve as an approximate example once it is operating, though its filament’s resistance changes as it warms.
The wattage on a label describes a rated operating condition, not necessarily what the appliance draws every moment. A thermostatically controlled heater, for instance, may switch its element off and on. Its current while heating is different from its current while the element is off. Actual household voltage can also differ somewhat from the nominal 230 V.
For motors, compressors, and some electronic appliances, simply dividing the printed watts by 230 V may not give their actual AC input current. Their electrical behavior can make input current different from this resistive-load estimate, and some draw extra current briefly when starting. Also keep the lesson-one distinction in mind: an adapter’s output wattage is not necessarily the wattage it takes from the wall.
Read the brief safety context and formula in the following resource. It explains why estimating current is useful, but a calculated figure alone is not permission to choose a cable, extension lead, or circuit protection.
Watts to Amps / Amps to Watts & Ohm's Law calculator / How to Calculate Wattage
Read Electrical Safety First’s “Amps, Watts & Volts Calculator” for its practical reason to relate watts and amps, and to reinforce which quantity you divide by which.
Under “Work out watts, amps and Ohm’s Law calculations in one place,” begin at “Knowing how to convert watts to amps is essential.” Read the safety context through the formulas beneath “Why it matters.” Focus on the stated limit on circuit current and the “Watts / Volts = Amps” formula.
That safety context matters, but today’s result has a narrower meaning: it is an approximate operating current for the specified appliance at 230 V. Later lessons will distinguish current calculations from decisions about household protection and safe responses to electrical problems.
Key takeaways
For a mainly resistive appliance, read its input power rating, convert kW to W if necessary, and estimate its current using
For example, 2000 W gives about 8.7 A while the appliance operates at that power. Treat the result as an estimate, particularly when an appliance cycles on and off, and do not assume the same simple calculation accurately describes every motor or electronic device.
In the next lesson, you will use an appliance’s power rating in a different way: to estimate electricity consumption over time, measured in kilowatt-hours.