# How to Measure Watt with a Clamp Meter?

To measure wattage (power) using a clamp meter, you need to perform a calculation because clamp meters typically measure current (amperes) and sometimes voltage (volts), but not directly watts.

Here’s how to do it:

1. Measure Current: Use the clamp meter to measure the current flowing through the conductor. Clamp the meter around one wire only (as shown in the picture above)
2. Measure Voltage: If your clamp meter has a voltage measuring capability, use it to measure the voltage across the load. If not, you will need a separate multimeter to measure the voltage.
3. Calculate Power: Multiply the current measurement (in amperes) by the voltage measurement (in volts). The result is the power in watts (W). Power (Watts) = Current (Amperes) x Voltage (Volts). Or use the calculator below

This method works for DC circuits.

For AC circuits, this calculation gives you the apparent power (in volt-amperes, VA), not the real power in watts, unless the power factor is 1.

If you need to measure real power in an AC circuit and the power factor* is not known, you will need a power meter or a clamp meter that can measure watts directly.

*Power factor is a measure of how effectively electrical power is being used, and it is defined as the ratio of real power flowing to the load, to the apparent power in the circuit.

In a perfectly efficient circuit, the power factor would be 1.0 (often expressed as 100%), meaning that all the power is being effectively converted to work.

However, in real-world applications, the power factor is less than 1. This is due to energy being lost, often in the form of heat. A low power factor indicates poor electrical efficiency, which can lead to increased energy consumption and higher utility bills.