# Finding the resistance of a resistor without multimeter

So this is a trivial but frustrating issue I’ve come across. I have two 5 band resistors and I am having a hard time differentiating the tolerance band.

I don’t have a multimeter on me and I don’t know if these are 1k (Brown black black brown brown) or 110ohms (Brown brown black black brown). Am I being completely oblivious to something?

Edit: I do know that the tolerance band is supposed to be at the end with the largest band spacing, but it looks equidistant to me.

• Just get a multimeter. Cheap resistors will be hard to read sometimes and this is a perfect example. Trying to work on electronics without a multimeter is a bit like trying to fly a plane in the dark without instruments. You're not going to get very far. A multimeter is your most basic, most important tool - full stop. You get an answer here in two seconds rather than spending half a day building some elaborate makeshift test rig to do the same job poorly. – J... Apr 1 at 16:19
• For what it is worth, you can get a serviceable (if a little slow) digital multimeter for less than 20 USD on Amazon or similar site right now. You should consider buying one. – user1850479 Apr 1 at 20:24
• Oh yeah for sure. I do most of my work in a lab but given the situation labs are closed and I didn’t want to add extra burden on shipping stuff when people are trying to get essentials in. Will place an order soon. Thanks – Jake Apr 1 at 21:56
• Reminds me of the time I had an inspector reject a batch of boards because the SMT 0603 resistors that should have been 560R were 195R. I took them back to him and turned the board around. – SiHa Apr 2 at 8:56
• Have a spare LED? 1 k vs 110 R difference will be visible. – skvery Apr 3 at 6:22

Use 9 V block and check if the resistor becomes hot.

P = U2/R. So your 110 ohms resistor should burn close to 1 watt. (Voltage of new battery will be > 9 V.)

• 1k! Thanks. Compared with a known 150. The150 got much warmer than this. If it was 110 I’m sure it would have been similar or warmer. – Jake Apr 1 at 9:55
• I'm sorry, but I don't agree with this answer, as is, since it's not broadly applicable and potentially harmful. What if the possible values are >10k? What if a future child reader tries this with a resistor that is some resistance that gets the resistor hot enough to burn them? – Charlie Apr 2 at 7:51
• @Charlie You had me until you mentioned children. Electronics should only be handled by responsible people. Either the kid is smart enough to be responsible and not do this, or not touch electronic projects at all. – Mast Apr 2 at 8:24
• A hot resistor is probably one of the safest ways to learn about not burning yourself on hot objects. – jpa Apr 2 at 17:01
• This is a terrible suggestion. Even if it does properly distinguish, e.g., 10 ohms from 1k ohms, the resistor itself is no longer useable after overheating like this. – Carl Witthoft Apr 2 at 19:01

Make a bridge. Feed it with low level audio signal and use a speaker as the detector. Headphones would be better than a speaker due higher sensitivity.

If R1/R2 = X/R4 the sound vanishes. Then X = R4 * (R1/R2)

In Wheatstone's bridge R1 and R2 are a potentiometer, R1/R2 is seen visually from the relative position of the slider. Originally DC voltage and sensitive galvanometer were used instead of audio and speaker.

• So it's really two voltage dividers. Slick. – Harper - Reinstate Monica Apr 1 at 19:13
• Other than getting a meter, this is the best answer so far. +1 – Charlie Apr 2 at 7:54
• I love this answer! I was going to suggest an A/C sweep source and a simple RLC circuit but this is simpler and more accurate. – Carl Witthoft Apr 2 at 19:02
• Even better, you can use a computer with sound card and actually measure a number with that. With only resistors in the circuit, you can't hurt it, as you'll only get less energy, not more. – The_Sympathizer Apr 3 at 15:38

These are 1k resistors, both black stripes are closer together than the two brown stripes on the bottom. The end with thicker and further apart stripes is the end with the multiplier stripe and the tolerance stripe. This is the rule with 5-band resistors, but due to how hard it is to tell them apart it is best to mark every resistor set with its value and measure using a multimeter. If you are calculating from the band colors, remember that resistor values most likely follow a value series, like E6 or E12. 110 is not part of the E6, E12 or even E24 series, but 1k is.

• This wins on "110 is not a standard size". – Harper - Reinstate Monica Apr 1 at 19:11
• This is just a great answer as an electronics amateur- I can now look through all my disorganised resistors and put them back in their home, thanks!. Although honestly the bridge answer is a great one too, and recommend it against the 'does the resistor get hot' solution. – mseddon Apr 2 at 15:06

You can build a circuit like

simulate this circuit – Schematic created using CircuitLab

Where RQ and C1 build an RC circuit. Take a watch and measure how long it takes for the LED to turn on. Compare with other known resistors.

• A 4.7 mF electrolytic capacitor usually has large tolerances. – Uwe Apr 3 at 17:34
• @Uwe: for a 100 Ohm resistor as in question, we need a large capacitor. Otherwise, time will be quite short and possibly not measurable with a wall clock – Thomas Weller Apr 3 at 20:20

5 band resistors have an extra (digit) band (3th) before the multiplier band (4th). Although a bit hard to spot (I never tried it myself), as described in this question you can start reading from the thicker band's side. So in your case it should be

$$110\ \Omega \ 1\%$$

Start reading from the end of the resistor where the color bands are closer together. In the picture, that appears to be brown-black-black-brown, brown. Or 1-0-0-1, 1. Which is 100 * 10^1, 1%. 1000 Ohms, 1%.

When in doubt, get a meter. For casual measurements, I have a digital meter I bought for under \$10 at a hardware store. That’s a very handy thing to have for kit building where it is difficult to distinguish colors or determine which are the thick and thin bands on resistors.

Yes, you can build yourself a Wheatstone bridge, but do you want to spend five minutes each time you check a resistor?

1k resistor. The broader band is tolerance, the spacing has nothing to do with it. When my older eyes can't see, I use my phone camera as well to magnify. That picture you took is perfectly clear. That is the way to do it for over 40's!

Assuming the resistors are not bad in some way and the only two values you are concerned about are 110 vs 1000, the first thing to note is that there is a lot of difference - a full order of magnitude - there. Hence it is not hard to break the tie.

Do you have a small incandescent lamp (by which I mean "electronic component-sized" lamp)? If so, by hooking it to, say, a 9 V battery in series with one or the other resistor will tell you right away, as the lamp will light much brighter when the series resistor is the 110 Ω one, as compared to the 1000 Ω one (it might not be visible at all with the latter at least in normal lighting, but should be with the former.).

This is, I'd say, a better idea than trying to get it "hot", because you don't want to risk cooking one or the other resistor. An incandescent lamp is a resistor that is designed to get hot :)