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Whether you’re pounding out a DIY project that will only ever see your backyard or designing a public monument, how to read a tape measure is a pretty universally useful skill. And though the simple tape measure may be the humblest of all tools, it’s arguably the most important for crafts where even an eighth-of-an-inch flaw can throw off your entire project. To set you up for success, we asked design experts the basics about how to read a tape measure—including what all those markings actually mean, the difference between metric tape measures and those that use imperial units, and how laser measures compare to that tape measure you got for a couple bucks off Amazon.
“A tape measure is absolutely crucial, whether you are measuring for a future piece of furniture or planning out something more detailed like a kitchen cabinet,” says Ming Thompson, principal of New Haven, Connecticut–based architectural firm Atelier Cho Thompson. “The worst certainly could happen; that expensive dresser just might not fit. Always measure twice.”
And no, that’s not just an architect being extra cautious because that’s what she has to tell students at the Yale school of architecture. North Carolina–based interior designer Heather LaBoda says a tape measure is often the first thing she reaches for when she’s working on a job, too, and that every homeowner with even a passing interest in DIY projects needs to learn how to use one. Deciding to “ballpark” measurements or work off of old architectural drawings without verifying may cost you in the long run. “You may find that your design doesn’t fit and [you] may need to make significant design changes to fix the issue, which could cost time and money,” LaBoda says.
Though a tape measure and a ruler look alike and serve the same purpose, you should have at least one tape measure at home at all times for most home improvement projects, as they can measure longer distances and are more flexible and accurate than the rulers you used to draw straight lines in grade school.
For measuring long distances it’s better to have a tape measure on hand than a ruler.
As simple as the concept seems, there are several components to a modern retractable measure that you should know before you use one.
Often, the hook of the ruler will be built with small holes, allowing the user to temporarily affix it somewhere to get an accurate measurement, sans another set of hands to hold it down.
The most important part of a tape measure is the blade, or the tape, which is the part the measurements are printed on. It’s usually a thin metal ribbon. Traditionally it’s painted yellow. The tape is typically 15 to 50 feet long.
The hook is a metal L-shaped piece that’s fastened to the end of the blade. Sometimes you’ll see a slot, or one or two smalls holes, in the hook. These are called “hook slots” and are there so you can affix one end of the tape measure to something, freeing you to extend the blade beyond arm’s reach. This is invaluable if you’re trying to measure something long and don’t have a helper to assist.
What your tape measure says can depend a lot on what part of the world you’re in. Despite the best efforts of President Jimmy Carter and a majority of scientists to get more Americans to use the metric system, most nonscientific linear measurements in the US are still based on the US Customary System.
So, though some tape measures will have increments in the decimal-based system of metric units—like millimeters, centimeters, and meters—the tape measures you see in the US almost always have increments in what are often (but technically, incorrectly) called imperial units: fractions of an inch, inches, and feet. Some tape measures have markings for both the metric system and the USCS system—the former commonly in red and the latter in black, at least in the US.
Note that though the USCS is historically related to the oft-considered obsolete British Imperial System and still often referred to as the “imperial system” or “imperial units,” they’re distinct systems with incompatible measurements for many things.
You may also want to know that on December 31, 2022, the US federal government officially retired the old “survey foot” definition of a US foot and adopted the international foot, which is almost microscopically shorter than the old US foot. It’s such a small difference that it won’t affect most people at all, but for those in professions dealing regularly with measurements in large numbers (as in miles or more), it can make a huge difference. So when we talk about a foot today, we’re actually talking about a slightly different length than (at least in the US) in 2022 and before.
When it comes to tape measures, though, you don’t need to worry about the switch to the “new” foot. In other words, your pre-2023 US tape measures will still work just fine.
In the US, the smallest marks are usually 1/32nds or 1/16ths of an inch. These are typically the shortest lines, spaced the most closely together. Next are the 1/8th of an inch markings, slightly but noticeably longer than the 1/16th-inch markings. 1/4-inch markings are the middle of the range, followed by 1/2-inch marks.
Then there are full-inch marks and foot marks, or even yard marks, which might consist of lines that span the entire width of the tape measure blade.
Did you pay attention in third grade when your teacher went over fractions? This is where it finally comes up, especially for USCS-based tape measures.
For example, your tape measure may, instead of marking a half-inch as “1/2” of an inch, mark it as “8/16” of an inch. So if you’re looking for a specific length on your tape measure and can’t seem to find it, try thinking of how it might be expressed in terms of smaller units, like sixteenths of an inch.
Mowat says that amateurs are most often tripped up by the fractions of a tape measure when taking measurements. “Especially when using the imperial system,” he says. “Is the 1/8-inch tick before the 1/2-inch mark or after? Is it 3/8ths of an inch or 5/8ths of an inch? Or maybe it’s 11/16ths?”
If you have a metric tape measure, it’s a lot more straightforward. The smaller markings are millimeters or centimeters. The bigger markings are decimeters or meters. Everything’s cleanly divisible or multipliable by 10.
On US tape measures that use both measurement scales, most use black notation for the USCS measurements and red for the metric. Don’t get them mixed up!
The red dots, sometimes red diamonds, are a shortcut marking to measure the standard distance between wall studs and joists: 16 inches on center. If you have a tape measure that includes these, you’ll notice red dots every 16 inches on the blade.
Black diamonds are the tape measure’s shorthand for the distance between studs or joists using the newer, more economical 19.2-inch-on-center framing standard.
The 19.2-inch standard is meant to reduce the amount of required lumber in construction without sacrificing structural integrity and allowing for spacing for builders to easily slide in US-standard eight-foot plywood or drywall sheets.
So if you have one of these tape measures, you’ll see black diamonds every 19.2 inches on the blade. Some tape measures have both red dots and black diamonds marked off so builders can switch easily between 16 inches on center and 19.2 inches on center.
It’s helpful to have a pencil or other marking tool on hand when taking measurements.
Using a tape measure is simple and intuitive once you get the hang of it.
Unless you’re measuring a distance that’s shorter than your arm span, taking a measurement is much easier if you have someone to help you.
Figure out what you’re actually measuring, as in what two points you’re using as the beginning and the terminus of your measurement. Mark them using an easily wiped-off instrument like chalk or a grease pen.
For most home uses, you’ll want to pick something you can measure straight and level—you’re not going to get an accurate sense of how wide a space you need for your new armoire if you’re including the curve of its outward-flaring doors in your measurement of the width.
Take the working end of the tape measure and fasten it, as necessary, to the point you’re measuring from. Or get someone to hold it in place if it’s going to be too far for you to do it all yourself.
Next, extend the tape until the exposed part of the tape reaches the point you’re measuring to. Keep the tape flat and straight. If you’re measuring a distance, keep it as level to the ground as you can.
“It’s important to keep your tape measure as straight as possible when taking measurements,” LaBoda says. “It’s easy to bend a tape measure, which can cause inaccuracies.”
Lock the measuring tape’s blade in place, using the thumb slide or lock.
Read the increment marking closest to the case. That’s the full measurement.
If you’re also trying to find the length of two points along the measurement, note the measurement of the first point you want to measure and then the second point and simply subtract the smaller number from the larger number.
No matter how wide and rigid your tape measure blade is, you’re going to find it challenging to measure the heights of most rooms’ ceilings with a tape measure.
Thompson uses a nifty trick of the trade: “If you’re trying to measure something tall, like a ceiling or the top of a window frame, don’t just extend the tape measure and attempt to hit the high point with the metal endpiece,” she says. “Instead, step on the metal endpiece, pinning it to the floor, and extend the tape into an upside-down U shape, with the highest point of the folded tape at the high point you are trying to measure. This takes advantage of the structural strength of the tape’s shape and creates a more stable and easy way to measure.”
LaBoda, Thompson, and Mowat all agreed that a 25-foot tape measure—the kind that’s the most commonly sold in hardware stores—would work as the mainstay of most homeowners’ utility closets. They also preferred one-inch or wider blades, since the extra stiffness makes the tape less likely to flop around when you extend it to longer lengths.
If you frequently pull out tape measures on the go, however, the 25-foot tape measure can quickly start to feel cumbersome. “For carrying around (if you’re a designer or just a person who loves measuring), a 16-foot tape in a plastic case is perfect,” Thompson says. “I also carry a tiny 10-foot tape in my pencil case at all times. It’s so narrow that it can’t span long distances on its own, but it’s good for flat measurements in a pinch.”
When Thompson was a designer for Apple Stores, her team measured to 1/32 of an inch—the smallest increment on a tape measure. But for the purposes of most DIY projects, the experts we consulted agree that accuracy to within a quarter inch is usually fine.
Though most tape measures are made of a flexible metal, it’s common to see cloth tape measures (or, if you’re building IKEA furniture, even paper). But if you want more accurate measurements, stick to metal. “When used correctly, a metal tape measure is more accurate than a cloth tape measure because its rigidity makes it easier to keep the tape straight,” LaBoda says.
If you’re working on a professional project or often have to deal with taking difficult-to-reach or unusually long measurements, consider investing in a laser measuring tool. “Everyone in my firm is required to carry a laser measure at all times—they come in handy every day,” Thompson says of her work.
A laser measuring tool can help with precision, but a number of environmental factors can cause it to fall short of a standard tape measure—like the light of the space you’re working in.
“First, make sure it’s set to start dimensioning from the back of the device—not the front, where the laser is located,” Thompson says. “You put the back of the device up against a wall, or floor, or other surface and hit the red arrow button (the only button on the machine) to generate a measurement.”
Under the right conditions, laser measuring tools can be more accurate and much faster than a manual tape measurement. They also make measuring larger rooms and ceilings much easier. Plus, you don’t need a second person to hold anything down.
Of course, there are a few drawbacks. They’re much more expensive than regular tape measures, so don’t be shocked to see prices from 6 to 25 times as much as your run-of-the-mill steel ribbon measure (which you can get for as low as about $5 on Amazon).
Some experts stick to only using laser measuring tools indoors.
A number of factors can make them less effective, like atmospheric conditions, the slightest shift in where you place it, and the kind of light you’re dealing with.
“If it’s a very bright day, they can be hard to work with,” Thompson says.
In fact, LaBoda generally only finds them useful inside and uses laser measures to complement, not replace, her tape measures. “Typically, measuring a space involves using a combination of laser and manual tools,” she says. “I typically use a laser tape measure for large architectural components and a handheld tape measure for smaller details and furniture pieces.”
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