What’s the difference between M, mm, ml, mil?

What’s in a name and abbreviation? Actually, a lot! Especially when it comes to measurements and the difference between M, mm, and ml and mil. The short version is that mm means millimeter (a length), ml means milliliter (an amount of liquid), mil means one thousandth of an inch (a thickness), and M is the Roman numeral for 1,000. As we dig in, one consistent thing you’ll notice is the prefix “mil” which means thousand or thousandth.

M

Let’s start with just plain M. In this context, technically M represents the Roman Numeral for 1,000. We’ve likely all seen smaller Roman Numerals on watch faces, but M is a little less common. Most often we see M used to indicate a specific year, usually on a building that wants everyone to know how long it’s been around. Informally, some people will also use M to signify million, but that’s more shorthand than an official abbreviation. Let’s take a look at M in action, shall we?

MMCXXXII = 2,132
$14.9M = fourteen million, nine hundred thousand dollars

mm

The abbreviation mm stands for millimeter, which is a linear unit of measurement within the metric system. The millimeter symbol is mm, two lowercase letters with no period required. Mil still means thousand, but in this case a millimeter is one thousandth of a meter. So it takes a thousand of those little guys to fill up an entire meter stick! Want to think about mm in an every-day context?

1 US dime = 17.91 mm in diameter (US Mint coin specifications)

On our product pages, mm is how neck size is measured. The first number in a neck finish code like 20-410 is the diameter in millimeters, and Matching Neck Finishes explains how to measure yours and why the lid has to match.

ml

The abbreviation ml stands for milliliter, a metric unit that shows up on a lot of liquid labels. If you’ve ever wondered what ml means in measurement (or whether it’s a unit, a typo or a very short Roman numeral), it’s a unit of volume, used for liquids. The abbreviation ml is typically pronounced M-L (saying the letters out loud) or milliliter, and you’ll sometimes see it written mL, which means exactly the same thing. This one is nice to remember. When you see the little “l” just think to yourself l = liquid. For this abbreviation, ml is one thousandth of a liter, so it’s a super small measurement. For context, we’ll look at one of our popular ml bottle capacities and your typical order from your favorite coffee place.

30 ml = 1.01 oz.
About 473 ml = 16 oz. Latte

Capacity in ml is common on small dropper and roller bottles, like the 15 ml G883AM amber glass Euro dropper bottle. If droppers are what you’re shopping for, Know Your Dropper Types sorts out the assemblies from the tips.

mil

So what is a mil? Mil (pronounced mill) is one thousandth of an inch, and it is not short for millimeter, even though it looks like it should be. (How dare they throw in Imperial measurements?!) Think of mil as a way to measure the thickness of flat objects like credit cards or walls of plastic objects like pails. For anyone who needs the conversion, 1 mil is 0.0254 mm, so 1 mm is a little under 40 mils. Some examples of mils would be:

Your typical credit card = 30 mils = 3/100 of an inch (ISO/IEC 7810 card thickness)
Item P058-PL (5 gallon pail) = 90 mils = 9/100 of an inch

That second one is our P058-PL white HDPE pail, and a 90 mil wall is about 2.3 mm of plastic, which is a respectable amount of plastic between your product and the loading dock. If bulk containers are on your list, you can browse all of our pails and drums.

How These Units Show Up on Our Product Pages

Once you can tell the four apart, spotting them in a product listing gets a lot easier, because each unit tends to live in one spot on the page. A neck size is in mm, a capacity is in ml and a wall thickness is in mil, so a spec sheet is really just a short quiz you’ve already studied for.

Not every listing uses every unit (plenty of bottles list capacity in ounces, and plenty of pails never mention a wall thickness), so if a number you need is missing, it’s fair game to ask.

Remembering Which Is Which

It’s tough to remember these when they’re all so similar. But it can help to break each word down. Think of the suffixes for mm and ml: meter and liter. That narrows it down. Then, M by itself is the Roman Numeral. Mil spelled out is the only measurement that uses an inch.

See? You’re already making things easier on yourself. Way to be.

If a spec on a product page still looks like alphabet soup, our team will happily read it with you at (800) 473-4144, and you can reach out to us here too. To start browsing in the units you now know, our glass bottles and plastic bottles are a good place to practice.