How to Measure Screw Size

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If you have some loose screws but need more of the same kind, then you will need to measure them. This way, you can make sure you get exactly the same size of screws when you go shopping for new ones. It’s pretty easy to do—all you need is a measuring tape or a ruler and the screws in question. Just make sure to measure the screws correctly using the imperial system or metric system, depending on how the measurements are listed on screws where you will be buying them. You can always do both just to be sure!

Method 1
Method 1 of 2:

Measuring Screws with the Imperial System

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    Wherever the screw head would rest when it is fully embedded in something is where you start the measurement. Use a ruler or measuring tape to measure from here to the tip of the screw. [1]
    • For example, a countersunk screw with a flat head will rest flush with whatever it is embedded into, so start the measurement at the top of the screw head. [2]
    • For a countersunk screw with a rounded head, also called an oval countersunk, you start the measurement where the oval top and the countersunk half meet in the middle. In other words, where the oval top would rest on the surface.
    • To get the length of round-headed screws that aren’t countersunk, start measuring from the flat underside of the screw head. [3]
    • You can also use a template to measure the length of the screws. [4]
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    Use a ruler or measuring tape to measure from one side of a thread to the other using the nearest fraction of an inch. This diameter for screws in the imperial system is represented by either a gauge number or in fractions of an inch. [5]
    • A gauge number for screws in the imperial system corresponds to a certain fraction of an inch in diameter. To figure out the gauge number for a certain diameter, or vice versa, you have to look at a gauge guide to match up the "#" of the gauge with a fraction of an inch. You can find these guides online.
    • For example, a #0 gauge screw is 1/16 of an inch in diameter, #1 is 5/64 of an inch, a #2 is 3/32 of an inch, and so on.
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    Lay the screw next to a ruler or measuring tape and hold it steady. Count the number of threads in the space of an inch to get the thread spacing for screws in the imperial system. [6]

    Tip : Screws sold with imperial system measurements on the packaging list the gauge first and the length next. They don’t usually list the threads per inch. For example, 10 x 2” means that the screw is a #10 gauge and is 2 inches long. If they include the thread count, it comes between the two numbers, like 10-35 x 2”.

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Method 2
Method 2 of 2:

Measuring Screws with the Metric System

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    Start measuring from wherever the screw head would rest on the surface when it is fully screwed in. Use a measuring tape or ruler to measure from here to the tip of the screw. [8]
    • Take into account the type of screw head when you are measuring, because different screw heads rest differently on surfaces.
    • For instance, a flat-headed countersunk screw will rest flush with a surface. Measure from the top of the flat head to the tip of the screw to get the length.
    • Round-headed countersunk screws only sink part-way into a surface, so the rounded top will stick above the surface. Start measuring from the bottom of the rounded top.
    • To measure any other types of round-headed screws that aren’t countersunk, measure from the flat underside of the screw head to the tip.
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    Use a ruler or measuring tape to measure from one side of a thread to the other in mms. This is how the diameter is represented for screws in the metric system. [9]
    • If you’re buying screws with the measurements listed on the packaging in the metric system, then the first number represents the diameter. For example 5.0 means the screws have a diameter of 5 mm.
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    Screws use pitch as a measurement in the metric system instead of thread spacing. Use a measuring tape or ruler to measure the distance from one thread to the next in mms to get this final measurement. [10]
    • The pitch of a screw is typically less than 1 mm, you would measure it as a decimal point of a mm.
    • Most screws in the metric system have 1 pitch that corresponds to each diameter. For instance, 2 mm screws have a pitch of 0.4 mm.

    Tip : Screws sold with metric system measurements on the packaging will list the diameter first and the length next. For example, a package of screws that says 5.0 x 60 means that the screws have a 5 mm diameter and are 60 mm long.

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Expert Q&A

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  • Question
    How do you determine the length of the screw you need?
    Gino Colucci
    Home Improvement Specialist
    Gino Colucci is a Home Improvement Specialist and the Owner of Crackerjacks Handyman Services (not a licensed contractor) in Chandler, Arizona. Crackerjacks Handyman Services offers an effective cost-saving solution for commercial and residential repair and maintenance needs, specializing in smaller projects. Crackerjacks Handyman Services carries liability insurance and all technicians go through a background check.
    Gino Colucci
    Home Improvement Specialist
    Expert Answer
    If the screw is meant to be countersunk, measure the entire length. If the head will be exposed, measure from the bottom of the head to the end point.
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      References

      1. ↑ http://hingedummy.info/screwinfopage2.htm
      2. ↑ Gino Colucci. Home Improvement Specialist. Expert Interview. 7 January 2021.
      3. ↑ Gino Colucci. Home Improvement Specialist. Expert Interview. 7 January 2021.
      4. ↑ Gino Colucci. Home Improvement Specialist. Expert Interview. 7 January 2021.
      5. ↑ https://www.boltdepot.com/fastener-information/machine-screws/machine-screw-diameter.aspx
      6. ↑ https://medium.com/jaycon-systems/screws-how-theyre-classified-and-how-to-know-what-kind-to-use-898f729b33c7
      7. ↑ Gino Colucci. Home Improvement Specialist. Expert Interview. 7 January 2021.
      8. ↑ http://hingedummy.info/screwinfopage2.htm
      9. ↑ https://www.diydoctor.org.uk/projects/screwsize.htm
      1. ↑ https://medium.com/jaycon-systems/screws-how-theyre-classified-and-how-to-know-what-kind-to-use-898f729b33c7

      About This Article

      Article Summary X

      If you have some loose screws and want to know if they’re the right size for a project, or if you need to get some duplicate screws of the same size, you can find out how big they are with a few simple measurements. Before you start, make sure you know whether you need to take the measurements in imperial or metric units. To find the length of the screw, line it up with a ruler and measure from the tip of the screw to the head. If the screw has a rounded head, measure to the flat part, where the screw will lie flush with the surface that it’s going to be screwed into. Measure the length in inches if you’re using imperial units, and in millimeters if you need metric units. To get the diameter of a flat-tipped screw, put the end of the screw against your ruler or measuring tape. Measure the width across the tip in either fractions of an inch or in millimeters. If you’re measuring in fractions of an inch, you may need to use a screw gauge chart to convert the measurement into a standard gauge size. For example, a 1/16-inch screw has a gauge of #0. On the other hand, if you’re using the metric system, the diameter of the screw is usually listed in millimeters. This means that a 5 mm screw would be labeled as 5.0 on the packaging. The final common measurement for screws has to do with the number and spacing of the threads, or the thread pitch. In the imperial system, you’d measure this by calculating the number of threads per inch. Line the screw up next to a ruler or measuring tape and count how many threads you see in the space of an inch. The most common pitch numbers are between 35 and 40 threads per inch. If you’re doing a metric measurement, check the distance between two threads instead. For example, a typical screw with a 2 mm diameter will have a pitch of 0.4 mm between each thread.

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