Microwave oven power test

This test is generally made only when a customer complains that the food appears to be under-cooked or takes a long time to cook thoroughly.

There have been a number of attempts to quickly determine if the oven is performing to its specified power. However, the simplest and perhaps the most reliable involve heating a known volume of water for a specified time, and noting the temperature change following the heating process.

There two arrangements for this type of test; JIS and IEC705.

The JIS system was originally provided for ovens manufactured up to 1990, while the IEC705 arrangement was established for ovens manufactured after 1990.

The IEC705 arrangement is aimed more at a laboratory environment where mains voltage and ambient conditions are controlled.


This test is designed to provide a guide to the general efficiency of the heating system and to indicate gross loss of power output.  It is not a laboratory test and as such has a wide toleerance in terms of results

Equipment required:

2 x 500ml plastic beakers
1 x Accurate thermometer
1 x Flat stirrer

  1. Fill each beaker with 500ml of water at 20 C° +/- 5 C°
  2. Check the precise temperature of each and if there is a difference find the average by adding the two values together and dividing the result by 2.
  3. Place the beakers in the centre of the cooking area and set the oven to full power and switch on. Allow the oven to operate for precisely 60 seconds, allowing 2 seconds for the magnetron to reach operating temperature.
  4. Remove the beakers from the oven and stir each beaker immediately before taking the temperature of each, repeating step 2.
  5. Subtract the average starting temperature from the average final temperature and multiply the result by 70 to give the value representing the oven power in Watts (JIS)


Starting temperature: (19.3 + 19.9) /2 = 19.6 C°
Final temperature: (27.1 + 30.5) /2 = 28.8 C°
Difference: 28.8 – 19.6 = 9.2 C°
Power output: 9.2 x 70 = 644 Watts JIS


  1. Proceed as for JIS test, but with water at 10 C° +/- 2 C°
  2. On reaching step 5, multiply the difference between the averaged values by 71.15 to give the power output in Watts IEC705


Starting temperature: (8.8 + 11.0) /2 = 9.9 C°
Final temperature: (19 + 20) /2 = 19.5 C°
Difference: 19.5 – 9.9 = 9.6 C°
Power output: 9.6 x 71.15 = 683.04 Watts IEC