How Are Screws Measured?

Screw Measurement, Explained

In this article, we'll explain the answer to the question, "How are screws measured?" Screws come in a wide range of styles and sizes for many construction purposes. Understanding how screws are measured will help to ensure you choose the correct one for your upcoming construction project.

Screw measurement is more complicated when compared with nails. If you choose a screw type that has the wrong length or width, it could potentially split the wood you're working with. Below, we'll discuss three important screw measurements that you should know to help you make the right choice for your project.

The 3 Screw Measurements

From woodworking to metal roofing, it will be helpful to have an understanding of three important measurement, namely screw gauge, length, and threads per inch. We'll introduce them here:

Major Diameter (in)	Threads per inch (tpi)	Major Diameter		Tap Drill Size (mm)	Pitch (mm)
Major Diameter (in)	Threads per inch (tpi)	(in)	(mm)	Tap Drill Size (mm)	Pitch (mm)
#1 - 64	64	0.073	1.854	1.50	0.397
#2 - 56	56	0.086	2.184	1.80	0.453
#3 - 48	48	0.099	2.515	2.10	0.529
#4 - 40	40	0.112	2.845	2.35	0.635
#5 - 40	40	0.125	3.175	2.65	0.635
#6 - 32	32	0.138	3.505	2.85	0.794
#8 - 32	32	0.164	4.166	3.50	0.794
#10 - 24	24	0.190	4.826	4.00	1.058
#12 - 24	24	0.216	5.486	4.65	1.058
1/4" - 20	20	0.250	6.350	5.35	1.270
5/16" - 18	18	0.313	7.938	6.80	1.411
3/8" - 16	16	0.375	9.525	8.25	1.587
7/16" - 14	14	0.438	11.112	9.65	1.814
1/2" - 13	13	0.500	12.700	11.15	1.954
9/16" - 12	12	0.563	14.288	12.60	2.117
5/8" - 11	11	0.625	15.875	14.05	2.309
3/4" - 10	10	0.750	19.050	17.00	2.540
7/8" - 9	9	0.875	22.225	20.00	2.822
1" - 8	8	1.000	25.400	22.85	3.175
1 1/8" - 7	7	1.125	28.575	25.65	3.628
1 1/4" - 7	7	1.250	31.750	28.85	3.628
1 3/8" - 6	6	1.375	34.925	31.55	4.233
1 1/2" - 6	6	1.500	38.100	34.70	4.233
1 3/4" - 5	5	1.750	44.450	40.40	5.080
2" - 4 1/2	4 1/2	2.000	50.800	46.30	5.644
2 1/4" - 4 1/2	4 1/2	2.250	57.150	52.65	5.644
2 1/2" - 4	4	2.500	63.500	58.50	6.350
2 3/4" - 4	4	2.750	69.850	64.75	6.350
3" - 4	4	3.000	76.200	71.10	6.350
3 1/4" - 4	4	3.250	82.550	77.45	6.350
3 1/2" - 4	4	3.500	88.900	83.80	6.350
3 3/4" - 4	4	3.750	95.250	90.15	6.350
4" - 4	4	4.000	101.600	96.50	6.350

1. Screw Gauge

The first type of screw measurement you should know is screw gauge. The screw gauge refers to the outside thread diameter of the screw.

To explain, screws with a gauge/diameter that is less than 1/4” are sized from #0 to #14. Meanwhile, screws with a 1/4" or larger diameter are sized by fractions of an inch. Also, the screw gauge has a decimal equivalent. With every screw size, it goes up by .013”. Below is a handy table to refer to for screw gauge measurements.

2. Screw Length

Next, we'll discuss screw length, or shaft length. For a countersinking screw, the length is determined by measuring the distance from the screw's head to its tip. This applies to flat-head, bugle-head, trim-head, and all other types of countersinking screws (where the screw head can be driven below the surface of the application.)

For non-countersinking screws, the measurement is determined by measuring from the bottom of the screw's head to its tip. For example, all hex-, pan-, button-, round-, and truss-head screws, this measurement applies.

3. Threads Per Inch (TPI)

Finally, we'll discuss the threads per inch for a screw. Otherwise known as TPI, a screw's threads per inch measurement refers to the number of threads in the 1-inch section of the screw.

As you are browsing for construction screws online, it is helpful to have an understanding of what threads per inch means. For example, in a screw's product name, such as "#10-12" this can be read as: "a screw with #10 gauge and 12 threads per inch."

Conclusion: How Are Screws Measured?

In conclusion, no matter the type of screw, its measurement can be taken in three different ways, 1.) by gauge, 2.) by length, and 3.) by threads per inch. Understanding the ins and outs of how screws are measured will help to equip you with the proper knowledge of which screw to choose for your construction project moving forward.

Jakes Sales has been providing quality metal roofing and construction screws online for many years. In fact, we are a trusted online source of many various types of wood and metal screws. When you choose Jake Sales to be your source of screws, you will enjoy the benefits of fast and FREE shipping to anywhere in the US (including Alaska and Hawaii), exceptional deals, and friendly customer service.

Have additional questions about how screws are measured? Looking for the proper screw type for your project? Please contact the knowledgeable team at Jake Sales by giving us a call at (406) 752-5253 and we'll be happy to assist you.