How to Measure Wood Screw Size

If you have some screws that are already in your project and you need more of the same size then you'll have to measure them to be certain you are ordering the exact same screws to match.

Measuring wood screws is a reasonably east task and can be accomplished with a measuring tape or ruler, and ideally a set of calipers. For this guide we're going to stick to imperial measurements, as most wood screws are sold in imperial measurements.

Step One: Measure from the tip of the screw, to where the screw head will rest when fully driven in to get the length.

Where to measure wood screw head

The three wood screws above each have different head types, a round head, flat head, and oval head. You can read more about the different head types and their uses here. The arrows in the image above indicate where each screw's length will be measured from. Measure from the sharp tip of the screw to where the head would naturally sit flush once the screw is driven in. 

  • For the round head screw on the left, the length will be measured from the flat underside of the screw head.
  • For the flat head wood screw the measurement can be started at the top of the screw.
  • For the oval head screw on the right the measurement will start where the oval top meets the angled countersink, right where the screw would rest flush when fully driven in.

This measurement is the length of the screw. The length has nothing to do with the gauge size, or number of the screw. We'll find that next.

Step Two: Measure the width of the thread to get the number, or gauge size.

Screw Measure # number or gaugeOn the left here we're using a set of calipers to measure the width of the thread to find the gauge size of the screw. The width should be measured across the threads, and not the unthreaded shank portion of the wood screw. However, the silicon bronze wood screws we have here at Fair Wind Fasteners have cut threads, so the unthreaded portion of the screw, or shank, is the same diameter as the outside of the threads. This is due to the screws having cut threads, and you can read more about that here. In the example in the picture, the measurement comes to 0.25 inches, or 1/4" since in the imperial system we love our fractions! Now when we go to the silicon bronze wood screw catalog we can shop around and find that the closest size is the #14 wood screws, so the screw in the photo on the left is a #14 silicon bronze wood screw. Alternatively, you can look in the handy wood screw size chart that we have here.

Now we know what size wood screw we have!

Step one gave you the length, and step two gave you the gauge size, or number of the screw. The number, as in #6, or #8 indicates the thickness or gauge size that we measured in step two. Now you can match what you have, to what you need to purchase.

Of course, you might not want to match the size exactly. Often when our customers are re-fastening a wood boat for example they might want to move up a gauge size for a tighter fit on those old planks and in those old frames. You may want to consider doing the same.

Have a poke around our Knowledge Base for more useful information about the quality fasteners we carry here at Fair Wind Fasteners. Maybe, for example, you want to know what size screws you need for that boat project. We can help with that and more!