How to Measure Screw Size

Co-authored by Gino Colucci

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

1
Measure in inches from the tip to where the screw head rests to get the length. 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]
X
Research source}
- 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]
  X
  Expert Source
  
  Gino Colucci
  Home Improvement Specialist
  Expert Interview. 7 January 2021.}
- 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]
  X
  Expert Source
  
  Gino Colucci
  Home Improvement Specialist
  Expert Interview. 7 January 2021.}
- You can also use a template to measure the length of the screws.^{[4]
  X
  Expert Source
  
  Gino Colucci
  Home Improvement Specialist
  Expert Interview. 7 January 2021.}
2
Measure the width of a thread in fractions of an inch to get the diameter. 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]
X
Research source}
- 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.
Advertisement
3
Count the number of threads in 1 inch to get the thread spacing value. 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]
X
Research source}
- Thread counts in the imperial system generally range from 35-40 threads per inch.
- The thread spacing is also called the thread pitch.^{[7]
  X
  Expert Source
  
  Gino Colucci
  Home Improvement Specialist
  Expert Interview. 7 January 2021.}
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”.

Method 2

Method 2 of 2:

Measuring Screws with the Metric System

1
Measure in mms from where the screw head sits to the tip to get the length. 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]
X
Research source}
- 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.
2
Measure the width of a thread in mms to get the diameter. 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]
X
Research source}
- 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.
3
Measure the distance from one thread to the next in mms to get the pitch. 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]
X
Research source}
- 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.

Expert Q&A
Did you know you can get expert answers for this article? Unlock expert answers by supporting wikiHow

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

Support wikiHow by unlocking this 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.