How to Measure Screw Size


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!

Part 1
Measuring Screws with the Imperial System

Measuring Screws with the Imperial System on How to Measure Screw Size

1
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] Different screw heads rest differently when they are screwed into something, so you need to measure them differently. 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. 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.

Measuring Screws with the Imperial System on How to Measure Screw Size

2
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.[2] 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.

Measuring Screws with the Imperial System on How to Measure Screw Size

3
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.[3]Tip: Screws sold with imperialsystem measurements on thepackaging list the gauge firstand the length next. They don’tusually list the threads perinch. For example, 10 x 2”means that the screw is a #10gauge and is 2 inches long. Ifthey include the thread count, itcomes between the two numbers,like 10-35 x 2”.Tip: Screws sold with imperial systemmeasurements on the packaging list thegauge first and the length next. Theydon’t usually list the threads perinch. For example, 10 x 2” meansthat the screw is a #10 gauge and is 2inches long. If they include thethread count, it comes between the twonumbers, like 10-35 x 2”.Tip: Screws sold with imperial systemmeasurements on the packaging list the gaugefirst and the length next. They don’tusually list the threads per inch. Forexample, 10 x 2” means that the screw is a#10 gauge and is 2 inches long. If theyinclude the thread count, it comes betweenthe two numbers, like 10-35 x 2”.Tip: Screws sold with imperial system measurements on the packaging listthe gauge first and the length next. They don’t usually list thethreads per inch. For example, 10 x 2” means that the screw is a #10gauge and is 2 inches long. If they include the thread count, it comesbetween the two numbers, like 10-35 x 2”.Tip: Screws sold with imperial system measurements on the packaging list thegauge first and the length next. They don’t usually list the threads perinch. For example, 10 x 2” means that the screw is a #10 gauge and is 2inches long. If they include the thread count, it comes between the twonumbers, like 10-35 x 2”. Thread counts in the imperial system generally range from 35-40 threads per inch.

Part 2
Measuring Screws with the Metric System

Measuring Screws with the Metric System on How to Measure Screw Size

1
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.[4] 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.

Measuring Screws with the Metric System on How to Measure Screw Size

2
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.[5] 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.

Measuring Screws with the Metric System on How to Measure Screw Size

3
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.[6]Tip: Screws sold with metricsystem measurements on thepackaging will list the diameterfirst and the length next. Forexample, a package of screws thatsays 5.0 x 60 means that thescrews have a 5 mm diameter andare 60 mm long.Tip: Screws sold with metric systemmeasurements on the packaging willlist the diameter first and the lengthnext. For example, a package of screwsthat says 5.0 x 60 means that thescrews have a 5 mm diameter and are 60mm long.Tip: Screws sold with metric systemmeasurements on the packaging will list thediameter first and the length next. Forexample, a package of screws that says 5.0 x60 means that the screws have a 5 mmdiameter and are 60 mm long.Tip: Screws sold with metric system measurements on the packaging willlist the diameter first and the length next. For example, a package ofscrews that says 5.0 x 60 means that the screws have a 5 mm diameter andare 60 mm long.Tip: Screws sold with metric system measurements on the packaging will listthe diameter first and the length next. For example, a package of screws thatsays 5.0 x 60 means that the screws have a 5 mm diameter and are 60 mm long. 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.