Wood Screw Size Chart: Find Your Needed Dimensions Now

Used in indoor and outdoor applications alike, wood screws are excellent alternatives to nails and wooden clamps.

They’re especially suited for mounting trim and hardware, clamping forms, and building jigs.

When using wood screws, it’s important to consult a wood screw size chart to guarantee you’re using the right size wood screws for your project. I’m here to help with just that.

In this article, you’ll learn how to read a wood screw size chart for all your wood screw needs.

Let’s dive right in!

How to Read a Wood Screw Size Chart

Wood screws serve a simple yet important purpose: securing two solid pieces of wood together without the need for cut joinery.

Unlike metal-working screws, wood screws aren’t threaded throughout. They have coarser threads with smooth shanks below the head.

The threads are usually only up to an inch in length.

The partially threaded design prevents the screws from turning when the thread runs out and protects the wooden material from splitting or cracking if the screws are driven in too far.

It also allows for a stronger, firmer hold overall.

Here’s how to properly read a wood screw size chart to help you choose the right wood screws:

Measure the Wood Screw Size

The size of a wood screw is determined by two major factors: shaft length and thickness/diameter.

This is the same for any kind of screw size chart you’re using; and it’s very useful!

The length and diameter, both of which are measured in inches, belong to a gauge group from 0 to 24.

Usually, the manufacturers list the wood screw gauge in the box itself.

If you don’t have the box, determine the size of your wood screw by manually measuring the width of a thread—in fractions of an inch—to get the diameter.

Then, consult the table below to determine the nearest fractional size of the screw you’ve just measured:

Screw Size	Nearest Fractional Size
No. 0	1/16″
No. 1	5/64″
No. 2	3/32″
No. 3	7/64″
No. 4	7/64″
No. 5	1/8″
No. 6	9/64″
No. 7	5/32″
No. 8	5/32″
No. 9	11/64″
No. 10	3/16″
No. 11	7/32″
No. 12	1/4″
No. 14	17/64″
No. 16	19/64″
No. 20	5/16″

Determine the Diameter Required

Once you’ve determined the wood screw size, check the wood screw’s minor, shank, and average head diameter.

The next set of columns corresponds to the appropriate diameter in both fractional and decimal measurements.

The minor diameter, also known as root diameter (RD), measures the smallest diameter of the screw thread.

On the other hand, the shank diameter measures the threadless part of the bolt between the thread and the head.

The head diameter measures the upper part of the screw.

Identify the Head Type

 

To accurately determine the head size, you’ll have to determine what head type your wood screw has.

Flathead wood screws, as the name suggests, have a flat top and a conically-shaped (cone-like) underside.

Oval head screws have a decorative top that slightly protrudes above the surface, but features the same conically-shaped underside.

Roundhead screws have a domed, round top and a flat head underside.

Double-Check the Screw’s Threads Per Inch

The wood screw’s threads per inch (TPI) ensure that the screw matches the part you’re inserting it into.

In general, higher-value TPI indicates a smaller thread pitch.

If the threading of a screw and nut are different, they’re either strip or seize the threading, resulting in improper and unusable connection.

Real-Life Wood Screw Size Chart Application

Let’s say you’re working on a wood project that requires merging two pieces of wood together.

First, you’ll have to determine the size of the wood screw you’re using by measuring the screw with a ruler.

If your screw measures 5/64 of an inch, your gauge screw falls under the #1 screw category.

From there, you’ll be able to determine the minor diameter and the shank diameter of the wood screw through the corresponding row.

For a #1 gauge screw, your minor and shank diameter size are as follows:

Screw No.	Minor Diameter		Shank Diameter		Average Head Diameter				Threads Per Inch
					Round Head		Flat & Oval Head
	Fractional meas.	Decimal meas.	Fractional meas.	Decimal meas.	Fractional meas.	Decimal meas.	Fractional meas.	Decimal meas.
No. 0	3/64	0.04	1/16	0.06	0.106	7/64	0.109	7/64	32
No. 1	3/64	0.046	5/64	0.073	0.13	44569	0.135	9/64	28
No. 2	1/16	0.054	3/32	0.086	12/30	5/32	0.16	5/32	26
No. 3	1/16	0.065	7/64	0.099	0.178	11/64	0.185	44636	24
No. 4	5/64	0.075	7/64	0.112	0.202	13/64	12/30	13/64	22
No. 5	5/64	0.085	1/8	0.125	0.227	7/32	0.236	15/64	20
No. 6	3/32	0.092	9/64	0.138	0.25	44565	0.262	17/64	18
No. 7	7/64	0.102	5/32	0.151	12/30	9/32	0.287	9/32	16
No. 8	7/64	0.112	5/32	0.164	0.298	19/64	0.312	44697	15
No. 9	1/8	0.122	11/64	0.177	0.323	21/64	12/30	11/32	14
No. 10	1/8	0.13	3/16	0.19	0.347	11/32	0.363	23/64	13
No. 11	9/64	0.139	13/64	0.203	0.395	25/64	0.414	13/32	11
No. 12	9/64	0.148	7/32	0.216	0.443	44758	0.48	31/64	10
No. 14	5/32	0.165	1/4	0.242	12/30	31/64	0.515	33/64	9
No. 16	3/16	0.184	17/64	0.268	0.539	17/32	0.602	19/32	8
No. 18	13/64	0.204	19/64	0.294	0.587	19/32	0.616	39/64	8
No. 20	7/32	0.223	5/16	0.32	0.683	44881	0.724	23/32	7

FAQs

How do I choose the right wood screw size?

To choose the proper wood screw size for your project, you need to check the screw’s length and thickness.

The wood screw should be long and thick enough to hold two boards together. It should enter at least half the thickness of the bottom material; i.e., 3/4″ into a 2 x 4.

How far should a wood screw penetrate wood?

A wood screw should penetrate the wood at a distance of about half to two-thirds of the screw’s threaded length.

Whether you’re building furniture, a tree house or need a deck screw chart for a backyard project, there are specific screw sizes to look into.

Conclusion

There you have it, folks; an in-depth guide on how to use and read a wood screw size chart!

Remember: whether you’re reading a machine screw size chart or one for bolts, you should always use the right wood screw size for your projects to prevent potentially disastrous accidents.

If your wood screws are too short and/or thin, they won’t properly hold the boards together.

If they’re too long, they’ll likely pierce through the other side of the wood.

Too-thick wooden screws split and damage wood, rendering it useless.

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