A fixed value which is used when converting meter readings to actual energy use, especially when potential transformers and similar types of equipment are used in metering. Since PTs and similar devices change the voltage into the meter, the measurement made by the meter represents only a fraction of the actual energy used. That fraction must be multiplied by the meter constant value to arrive at an accurate value for the customer's actual energy use. For example, if a commercial site receives 2,400 volts of electricity from the distribution network and their meter is designed to handle only 240 volts, a potential transformer may be used to divide meter voltage by ten. The meter reading will need to be multiplied by 10 to calculate that customer's actual energy use.

Meter constants may also be used to adjust readings taken from older meters which have been determined to be consistently inaccurate.

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