Wood Screw Sizes Chart

When using wood screws, the task appears simple. However, there is more to getting the right screw than picking a screw that fits through a hole. You may need screws where you drill pilot holes as the shank diameter is too large to screw directly into the wood.

Besides this, you could accidentally use sheet metal screws that won’t properly grip the wood. After all this, there are the threads per inch and the different head types. You no longer have a flat head screw; you can have a slot head, Philips, and even hex head screws.

In our guide, you can find the wood screw length chart to help get the right screw for the thickness of the material. By the end, you’ll see how helpful the screw diameter chart is for the measurement of screws you need after drilling. (Learn How To Screw Into Concrete)

Wood Screw Sizes

What Are The Sizes Of Wood Screws?

Wood screws range in size from #0 to 24 inches, with #0 being the smallest and #24 being the largest. The sizes #11 to #14 are popular, although there is more to it than picking the most common sizes.

Screw Acronyms

Screws come in a huge variety of types besides the screw diameters, major diameter, gauge size, and more.

If you go to the hardware store, you’ll find many screws containing acronyms on the pack, which determine what they are.

  • ST- Self-tapping: Screws lack the need to drill pilot holes.
  • TT-Twin thread: Two threads means that a screw can be placed and removed faster than a single thread equivalent, making it more secure.
  • TFT-Twin Fine Thread: They have finer thread than non-fine thread screws; thus, they may easily fit into drilled holes.
  • ZP-Zinc Plating: It offers protection against corrosion.
  • ZYP-Zinc and Yellow Passivity: They feature two layers of protection and are named for their yellow coating.

Imperial and Metric Screw Sizes

Sizing the proper screw in both metric and imperial units might be challenging unless you are familiar with the various screw sizes listed on the packaging.

You can learn the various screw sizes and see how converting from metric to imperial sizes is easy using our screw size chart.

1. Imperial Screw Sizes

Two numbers size a screw for wood: the first is the screw’s gauge, which is its shank diameter. This signifies that the major diameter increases as the number increases. As a result, a screw with the number 12 is larger than one with a number 4.

It’s crucial to remember that the gauge of an imperial screw has nothing to do with head shapes or size.

Although some sources may lead you to assume that this is how the gauge is computed, the gauge is nearly twice the diameter’s head from screw gauge 6 and up is purely coincidental.

It’s worth repeating that the length specified for a screw is the length buried in the wood or other material, not the underside of the head of a raised screw. The length and gauge of the screw define its size.

One final thing to remember is you can have fractional size used for the shank size and screw size in general. (Learn How To Remove A Rusted Screw With A Stripped Head)

2. Metric Screw Sizes

Though the metric system is straightforward to grasp for the untrained, it might be difficult if you are unfamiliar with it or are still working in imperial.

Instead of employing a “gauge” table, the metric system employs the diameter in millimeters. The length is measured in millimeters, the same as the imperial system.

The gauge happens to be about the same size as the screw head in millimeters by chance. A 6 gauge screw has a head that is nearly 6 mm broad.

The relationship between head size and diameter (metric in mm), gauge (imperial), and gauge (metric) is intricate. Yet, you’ll never find information to assure you the head size relates to the shank diameter.

The screw head’s imperial diameter is measured in 16ths of an inch and is double the gauge of imperial. Apply the formula below to calculate an approximation of the screw head diameters and gauge.

Head diameter in sixteenths of an inch X 2 – 2.

Gauge = the Head diameter in sixteenths of an inch X 2 – 2.

As an example, 5/16 head multiplied by two equals 10, and minus two equals 8. The gauge is set to an 8 screw diameter.

Using this formula, the diameter in mm for the imperial gauge is nearly half the gauge.

Imperial Screw Sizes

How Do You Determine The Size Of A Wood Screw?

A screw’s diameter is calculated by dividing the length from outer thread to outer thread in the opposite direction. Therefore, a screw’s largest diameter is frequently the correct size.

Screws occur in different sizes, but the three most commonly found are described below.

#6 Screw Diameter

Although the #6 screw is not the smallest, it is frequently used to assemble small objects. The thread diameter of the #6 screw is 0.13′′ (9/64th of an inch). #6 screws are available in lengths ranging from 12′′ to 1-112′′.

Hinges, drawer slides, light-duty fixtures, and other minor tasks typically use them.

#8 Screw Size

This size is the most typical way to put various wooden pieces together. The thread diameter of the #8 screw is 5/32 of an inch, or 0.16′′.

It’s a multi-purpose screw commonly used in furniture, light construction, cabinets, and other applications instead of nails. You’ll find these in lengths of 5/8th of an inch to 3′′.

#10 Screw Size

Because the #10 measurement is larger, it is used for heavy jobs. A #10 screw has a thread diameter of 0.19′′ (3/16th of an inch).

This type of screw is commonly used in building projects. However, they can also be used to assemble large furniture, as well as outdoor or patio furniture. They come in lengths ranging from 34′′ to 4′′.

Other screw dimensions can be found in the wood screw size chart.

Wood Screw Size Chart

Screw SizeThread Diameter
(in Fraction)
Major Diameter
(in inches)

What is a Wood Screw?

The wood screw has a head that fits a specific screwdriver, such as flathead or Philips. The shank is below the head and can vary in length from less than an inch to many inches. The shank is tapered to make driving into the wood easier.

The thread on the shank holds the screw in place after being driven into the wood. The wood screw has a benefit over the nail in that it may be withdrawn by reverse drive. The thread also secures the screw in the wood better than a nail.

Also, compared to sheet metal screws, a wood screw has less threads.

Types of Wood Screws

Different Types of Wood Screws

The uneven thread form of the original wood screws distinguishes them. New manufacturing technologies enabled the widespread production of wood screws with even threads by 1760. Advanced tools were created during the mid-1800s to make the screws more consistent across different sizes and head shapes. (Read Torx Screwdriver Sizes)

Screw Head Types

The most common wood screw is the flathead, which has a flat top and a tapering (conical) underside towards the shank.

  • Countersink the screw top to ensure it is flush with the material.
  • Roundhead and Panhead wood screws have rounded tops and flat bottoms. The heads of these screws may protrude from the material or sit inside a counterbore.

The wood screw comes in various thicknesses and length of the screw varies.

Parts of a Wood Screw

The wood screw measurements are divided into four pieces. The standard screw size varies by country or location. While metric screws are the most common, American screws use the Unified
Thread Standard.

Thread Diameter Size

A thread diameter is shown by a numerical system and each number represents a specific thread diameter.

For example, 9/64th or 0.13′′ thread diameter is #6.

The thread diameter ranges from #0 (1/16th inch) to #14 (1/4 inch). Depending on the chart, they may be larger.

Root Diameter

The root diameter comprises the threaded shank. The thread’s inner groove approaches the shank’s root diameter. This is roughly similar to a core diameter in a threaded hole.

The root diameter of the screw is less essential than the thread diameter because it is standardized based on the outer diameter and pitch.
Depending on how much material the screw root will occupy, it may be necessary for some.


This is the screw’s fundamental length. So a half-inch screw will be half an inch long.

Screw Length

Also, notice that the length of a flathead screw is measured from the top of the flat to the bottom of the screw, but the total length of a Panhead or rounded head screw is measured from underneath the head to the shank.

Head Size

This is the diameter or radius of the screw head type. The diameter of the head varies depending on the screw size.

Some feature wide heads, allowing a flathead or Philips screwdriver. Others have a smaller head to blend in better with the wood.

What Diameter Is A No 8 Wood Screw?

Screw SizeNear
Fractional Size
Hard Wood
Straight Pilot Bit
Soft Wood
Straight Pilot Bit

Screw Length

Screw length requirements are not set in stone. Due to building intricacies, you may not have many options in length.

The screw should travel through the narrower section and into the thicker piece. Then, thread about 2/3 of the screw into the “secondary” portion.

With thicker wood, this ratio can be lowered such that just half of the shank threads into the secondary piece. For example, on 1 in. and longer screws, only 2/3 of the shank is threaded.

Head Types

Flathead, roundhead, and Panhead are the three fundamental screw heads. Flathead screws should be countersunk flush with the wood. Before driving the screws, countersink the hole. An updated version of the flathead screw, the bugle head screw. It is designed to pull down flush with the surface.

Wood Screw Heads

A bugle head will pull flush in softwoods but somewhat above the surface in hardwoods. These screws have sharp nibs below their heads to cut away wood as they are driven. They work well in hardwood.

These screws don’t need to be countersunk. The circular top protrudes from the wood. Screws with round heads are standard. Panhead screws are like roundhead screws, but with a flattened top that doesn’t protrude as far.

Screwdriver Types

Screws often include recesses in their heads for three screwdriver types: straight blade, Phillips, and square. Slotted-head screws are those that require a straight-blade screwdriver. The oldest screw kind. Slotted-head screws function well when driven by hand but not well with a power screwdriver.

The Phillips head screw has a cross-shaped recess. As a result, the bit doesn’t jump off the screw head as quickly with this variety. Phillips-head screws are becoming more common as power screwdrivers become more common.

The square-head screw’s head is square. Although less common than Phillips-head screws, it is gaining popularity among woodworkers because of its superior screwdriver grip. Other screwdriver designs exist; however, they are now employed mainly in industrial applications.

Thread Types

The typical type of screw thread pattern was created a century ago because of the constraints of thread-cutting machines. As a result, it has two flaws: a two-step pilot hole, one for the threaded section and one for the shank. Second, the threads are shallow, limiting the screw’s holding power.

Wood Screw Dimensions

Because of their deeper and sharper threads, woodworkers often use a new form of wood screw is swiftly gaining popularity. The deep, sharp threads of the case-hardened extruded-thread wood screw. (Learn How To Magnetize A Screwdriver)

They cut quickly and hold well. In addition, the screw shank matches the threaded portion of the root diameter, allowing for a single-sized pilot hole.

Because these screws were initially used to attach drywall in building construction, they are commonly referred to as drywall screws.

Initially only available in black, these screws are now available in various plated finishes. These screws can be used in softwood and plywood without a pilot hole. Even for hardwoods, drill a pilot hole.

Wood Screw Sizes Chart

Leave a Comment

Your email address will not be published.