How to determine resistor face value

How to determine resistor face value

Determine the face value (resistance) of the resistor, having attached to it an ohmmeter. If there is no ohmmeter, attach the resistor to a current source, measure tension on it and current in a chain. Then calculate its face value. Besides, the face value of the resistor can be calculated on color scale or by the special code.

It is required to you

  • For determination of face value take an ohmmeter, the ampermeter, the voltmeter, tables of interpretation of face value by codes and in the flowers.


1. Determination of face value of the resistor direct measurements. Take an ohmmeter, attach it to resistor conclusions, having measured its resistance. For the correct measurement expose sensitivity of the device. If there is no ohmmeter, collect the electrical circuit including the resistor and the ampermeter. Parallel to the resistor attach the voltmeter. Then connect a chain to a current source. Learn value of current in amperes, using indications of the ampermeter and tension in volts, using indications of the voltmeter. Divide value of tension into current and receive the nominal resistance of the resistor (R=U/I).

2. Determination of face value of the resistor by codes or multi-colored markings. Attentively consider the resistor. If it is marked by three figures, then the first two designate dozens and units, and the third degree of number 10 by which it is necessary to multiply the number received from the code. For example, if code 873, then it means that number 87 needs to be increased on 10^3. Receive nominal resistance of 87000 Ohms or 87 kOhm. Similarly, if the resistor is marked by four figures. The first three make number, and the last – number 10 degree by which increase it. For example, the face value of resistor 3602 is 360•10²=36 kOhm.

3. In case the resistor is marked by two figures and one letter, use the special table of marking of SMD resistors of EIA in which will correspond to the first two figures numerical value of resistance, and a letter – number 10 degree. For example, to find resistor face value with marking 40C, 255 increase by 10² and receive resistance of 25.5 kOhm.

4. If multi-colored tags or rings are applied on the resistor, take the table of designations of nominal resistance on color. Basic rule: begin to consider from an extreme tag, the first three designate a mantissa, the fourth - number 10 degree, the fifth - admission on the resistor. For check use the special program of determination of face value of resistors.

Author: «MirrorInfo» Dream Team