# Any ideas on this resistor size?

I’m new at this…

20 kOhm?
But which power / watt rating?

0.125W, 1/8W
or
0.25W, 1/4W

Any assistance is appreciated.

Hello,
Welcome to the TechForum.The wattage for a resister needs to be calculated the same way the resistance in a circuit is we have online help, in the conversion calculators under the Ohm’s Law Calculator. The calculator is explained, and examples given on the website.

Link to the page Ohm’s Law Calculator | DigiKey Electronics

No worries, clinttaft.

We all need to start somewhere.

Based on the picture, I would estimate that you have a 10 kΩ, ¼ W resistor. However, there is only so much you can tell from a picture, and I could be mistaken.

Let me show you how to determine for yourself.

First, let’s look at the color. Digikey hosts a calculator that will allow you to determine the resistance for these 4-band devices. In this picture I have entered the colos as interpret from your original posting. However, I could be mistaken. You will need to select the colors as necessary.

That’s a good start but it’s only half of the question. We now need to determine the resistor wattage based on the physical size. From the picture, I can tell you that this is a metal film resistor. This style of resistor is manufactured by placing a thin metal film on a ceramic rod.

Here is a side-by-side comparison of a 1/2 W and a 1/4 W resistor.

For even more precision, we can refer to the manufacturer’s data sheet. There is a datasheet for nearly every component DigiKey sells. Each datasheet is a document that provides detailed electrical and mechanical specification for the component.

Here is a datasheet for one supplier of metal film resistors. It is 17 pages long. The information you seek is contained in this graphic as found on page 3 of the datasheet:

When you know the physical size, you will need to work backwards to determine the resistor series. For example, let’s assume the resistor measures 6.3 mm in the “L” dimension. The table indicates that this is a MFR-25 series resistor. We then go back to page 2 and see that the 25 field indicates a 1/4 W resistor.

Welcome to the world of electronics. It is sometimes overwhelming. However, things do get easier with time. Personally, I find it to be a very rewarding lifetime hobby and occupation.

Best Wishes,

APDahlen

P.S. To learn more about resistors your will certainly want to read DigiKey’s Resistor Reference Guide. It contains a wealth of useful information. you can find it and several other eBooks here.

1 Like

Thank you both so much! This helps tremendously.

1 Like