Klein Tools MM400 Multimeter Review


Editor Rating: 4.3/5


Klein Tools MM400 Multimeter

Reviewed by: Timothy Henderson

Last modified: Jan 25, 2023 @ 9:11 am

  • Design
  • Functionality
  • Price

Klein MM400 Review Summary:

What makes a good multimeter? Is it the design? The features? Well, the most important factors of a quality multimeter are accuracy, good resolution, and usefulness. If you find a multimeter useful, it doesn’t matter what kind of features it has to offer, as long as you’re satisfied.

Take a moment and read ToolNerds full review of the Klein Tools MM400 multimeter. 

Klein Tools MM400 – The Basics

When it comes to affordable multimeters, the MM400 is near the top. It has most of the features one needs for conducting various measurements, diagnosis, and repairs. The design is also pretty neat, and it comes with a rubber holster which ensures a better grip. The unit can withstand a drop from three feet of height thanks to the rubber protection. It measures up to 600V AC and DC, up to 10 amps of current, and up to 40 Ohms of resistance.  It can also measure temperature, frequency, capacitance, continuity, diodes, and duty cycle.

As you can see, versatility is not a problem for the MM400 multimeter. In fact, it’s suitable both for professionals and hobbyists, and that’s a pretty rare situation in the “Under $50” multimeter category.

The Klein MM400 Features

Auto ranging

This feature is one of the important ones. It is especially useful for people who aren’t experts when it comes to handling a multimeter. The function works on a simple concept – it sets the range automatically instead of you having to set it up manually. While it’s not a big deal for professional electricians, inexperienced individuals greatly appreciate this option.

Measuring temperature

The Klein Tools MM400 can measure temperature beside capacitance, voltage, and other electricity-related things. It’s not a standard function in this category, and that’s why it deserves to be mentioned. The way you can measure temperature is pretty simple. You’ll get a probe with the multimeter, and all you need to do is connect it properly to the unit. After setting up the multimeter put the thermocouple against the surface that you want to analyze. You’ll get a temperature reading after a couple of seconds.

The display

The screen is readable and big. You won’t have a problem to distinguish certain symbols or numbers. Many models from the “Under $50” category have some issues with the display, whether it’s the readability or lack of backlight. However, this particular model has a surprisingly good display without any major issues.

Low battery indicator

While it’s a standard function in most multimeters, it’s worth mentioning the benefits of the low battery indicator. How many times did you try to turn on your instrument and found out the battery is empty? The answer is probably – a lot of times. Well, those days are over thanks to this feature. The unit will issue an audible signal which should warn you about the low battery. As soon as you see the symbol on the screen – change the battery.

Auto shut off

In addition to the low battery indicator, the MM400  also has the auto shut off function. Its purpose is to preserve battery and prolong its life. A lot of people simply forget to turn off the multimeter after use, and that leads to unpleasant surprises such as an empty battery. However, you don’t have to worry about draining the battery thanks to this function. The device will turn off after 15 minutes of inactivity.

Data hold

This feature is another useful one. If you don’t have the time or opportunity to write down the values, press the “hold” button and the device will store the last reading until you overwrite it or press the button again. It helps in tight and urgent situations.

The MM400 design

One thing you’ll notice right away is the hit-resistant design. The unit has a rubber holster to ensure a better grip and to protect the multimeter from falls and bumps. The rotary switch is smooth, which is a pretty impressive thing because most multimeters have a switch which is pretty hard to rotate even when you’re holding the unit in one hand. However, you can rotate this particular switch single-handedly. If you want to change the batteries or the fuse, take the rubber protection off, and you’ll see an easily accessible battery compartment.

Who Can Use The MM400 Multimeter?

One of the greatest upsides of this model is the fact that it can be used by both professional electricians and people who just want to extend their toolbox inventory. The most impressive thing is that it still stays affordable while having a bunch of premium features such as the temperature mode, battery saving, and so on. Whether you’re dealing with electricity on a daily basis or not, you’ll certainly like the things this multimeter has to offer.

The beginners love its ease of use and usefulness, while the professionals appreciate its accuracy and precision. Either way – it’s a win-win situation. It might not be suitable for absolute beginners, but as long as you follow the instructions from the user manual, you shouldn’t have an issue whatsoever.

Klein tools mm400 use

MM400 Pros:


Easy to use




Great display with a backlight


A lot of additional features


Durable and sturdy



No True RMS technology


The screen may lose contrast under certain angles


Not suitable for checking sensitive electronics due to fluctuations in accuracy

Things We Didn’t Like About The MM400

There aren’t many shortcomings when it comes to this unit. However, we’ve noticed some minor things that should be mentioned so that you know what to expect.

The first thing you’ll notice is the lack of True RMS accuracy. However, it may be considered as a feature of more expensive multimeters, the absence of it is pretty noticeable. It mainly lacks a bit of range and accuracy. On the other hand, the minor reading fluctuations aren’t an issue if you’re using this multimeter for home use. However, if you’re a professional electrician, you might have a problem with it.

The displayed numbers lose contrast under certain angles. Although it’s not a thing that happens all the time, holding this unit under a particular angle will lower down the contrast of the display. Also, the backlight is pretty bright which contributes to the loss of contrast.

Kleintools mm400 review

Klein Tools MM400 FAQs

Is the MM400 a complicated multimeter?

Not at all. It can be used by anyone as long as you follow the instructions from the user manual. In fact, read the manual before using the unit regardless, because you’re dealing with electricity which can cause fatal injuries in most cases.

Does the MM400 have the “hold” function?

Yes, it does. It comes in handy if you aren’t able to write down or memorize the values.

Can I measure temperature with the MM400 multimeter?

Yes, you can. The thermocouple is included with the Klein MM400 multimeter.

Where is the MM400 multimeter made?

The Klein Tools MM400 is assembled in China.

Is it hard to replace the batteries on the MM400?

No, it is not. You need to remove the protective rubber holster, and you’ll see the battery compartment which is easily accessible.

What Users Say About The Klein Tools MM400

The general opinion about the MM400 is quite positive. In fact, it has only a few negative reviews on Amazon, and those are mostly from people who don’t know how to use the multimeter properly and have never heard about ghost voltages. However, if you’re a professional who is dealing with electricity on a daily basis, you should look for a more precise unit. While this one has a lot of auxiliary features suitable for professionals, it lacks a bit of precision due to the absence of True RMS technology.

The 4.3-star rating on Amazon shows that this product is certainly worth checking out.


If you purchase the Klein Tools MM400 multimeter you’ll get a decent instrument with a lot of additional options for an affordable price. If you’re looking for something impressively accurate for professional use, you might want to check out some other ones from a higher class. If you aren’t dealing with sensitive electronics all the time, there is no reason to skip this unit.

If you aren’t interested in the Klein Tools MM400, feel free to check our other multimeter reviews, and you’ll have a better chance of finding a suitable meter for yourself. As far as this one goes, it’s compact, lightweight, and perfect for DIY enthusiasts.

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