How to Calculate a KVA Rating

Equipment, such as computer servers, may require a power supply rated in KVA.
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Electrical or electronic equipment comes with electrical rating and operational parameters on the nameplate. It's often advantageous to convert this information into more useful information. For example, if you are looking for power in Kilovolts-amperes or, "KVA", the nameplate can provide information on voltages, amperes, power in watts, power factor or some combination. You can use simple power relationship formulas to convert known information into KVA.

    Calculate power rating in kilovolts-amperes, or "KVA," when you know voltage and current rating. Use the formula: P(KVA) = VA/1000 where P(KVA) is power in KVA, V is voltage and A is current in amperes. For example, if V is 120 volts and A is 10 amperes, P(KVA) = VA/1000 = (120)(10)/1000 = 1.2 KVA.

    Calculate power rating in KVA when you know voltage and output resistance. Use the formula: P(KVA) = (V^2/R)/1000 where R is resistance in ohms. For example, if V is 120 volts and R is 50 ohms, P(KVA) = V^2/R/1000 = (14400/50)/1000 = 288/1000 = 0.288 KVA.

    Calculate power rating in KVA when you know power in watts and the power factor. Use the formula: P (KVA) = P (watts)/pf where pf is the power factor of the power supply. If P is 12 watts and power factor is 0.86, P(KVA) = P(watts)/pf = 12 watts/0.86 = 13.95 KVA.