How Much Weight Can A 1/2 Inch Lag Bolt Hold? (Find Out Now!)

Heather Robbins
by Heather Robbins
Lag bolts are a key part of construction due to their ability to hold a lot of weight. We all know that ½” lag bolts can hold plenty of weight, but few are aware that they can exceed 20,000 pounds. Follow along as we explore exactly how much weight lag bolts can hold.

When it comes to any type of construction project, lag bolts are a must. You need to know how much weight a lag bolt can hold so you know which one is correct for your project. To demonstrate, we’ll tell you how much weight a 1/2 inch lag bolt can hold.

A 1/2 inch lag bolt can hold 21,285 pounds. There’s a particular calculation that goes into that, which we’ll get into further in this article.

Let’s dive into this information to learn more about lag bolts, how much weight they can hold, and how to choose one that’s the right size for your project.

What Is A Lag Bolt?

There are few screws that are as tough as lag bolts. These screws, also called lag bolts, are usually used to connect heavy wood and other heavy materials.

Unlike wood screws, sheet metal screws, self-drilling screws, and other more common screws, these screws are entirely different. Screws each serve a specific purpose, although they overlap in some cases. Lag bolts and screws have parts of their shaft without threads, so you can see this when looking at them.

Near the head of the screw, this usually has a variable thickness. The lag section, which generally makes the screw unique, is responsible for the screw’s unique properties. Since it cannot be threaded, the unthreaded portion of the screw will be subjected to massive compression forces when it is tightened. It results in a more tightly bonded material, which means it will resist more forces.

Why Is It Called A Lag Bolt?

They were initially used for securing barrel staves, also known as lags, which gave them their name. A lag screw requires an identically sized hole to its shaft. A gimlet point facilitates the process of placing the screw in the hole and threading it.

How Much Weight Can A Lag Bolt Hold?

Different lengths of the lag bolt will hold more weight than the nail that will hold up to 20 pounds and the screw that will hold up to 100 pounds inserted into the same stud:

  • Up to 100 pounds of pressure can be applied per inch of thread on 5/16-inch lag screws.
  • A lag screw measuring 3/8 inch can withstand up to 200 pounds per inch
  • A screw with a thread diameter of 14 inches will hold over 272 pounds

We know from experts that the smaller the screw or bolt, the stronger it will be. If you try to use a 1-inch screw to hold less than 100 pounds, your medium might be damage. Therefore, you would use the smallest available lag bolt if you wanted to anchor an entertainment system.

How Much Weight Can ½-Inch Lag Bolts Hold?

It is unnecessary to use a half-inch lag screw, and you are causing the joist to be compromised – for no good reason at all. An increase to 3/8″ places the pull-out value over 200 pounds per inch in most lumber using a 5/16″ lag screw.

Accordingly, the breaking load of a 1/2-inch grade 8 bolt with 13 threads per inch is equal to 0.1419 square inches (area subjected to stress) x 150,000 (tensile strength) = 21,285 pounds.

What Are Lag Bolts Used For?

There are many other materials that use bolts that can handle a lot of weight, besides roofing and lam beams. Take the case of building a deck: A deck provides hours of outdoor fun, the chance to cook outside, and a place to gather with friends. Houses with these features are worth more.

What is the best way to secure a deck to a house? A surface of the deck will be built upon joint surfaces attached to the house. Lag bolts secure the joints.


A number of houses, offices, storage units, and other buildings are constructed of concrete. Decks can be attached to concrete walls with lag bolts.

In a drilled hole, lag shields are concrete anchors that expand near the bottom to hold the shield in place. This type of screw is specifically designed for use with masonry materials.

Steel And Metal Roofing

Stainless steel is a trend in buildings now. For buildings with more than two floors, an I-beam is used when the wooden beam cannot support the weight. The carbon increases the tensile strength of steel, so it will not crack like iron.

Steel is a combination of iron and carbon. Metals other than stainless steel will not corrode as well as stainless steel. Corrosion-resistance is synonymous with stainless steel. Using stainless steel beams and joints, how do you attach them, so they support the weight? There are lag bolts involved, of course.

Metal sheets can also be used for building. Roofing materials often consist of this material. It is a roof made of galvanized, zinc-coated steel covered with layers of aluminum, zinc, and silicon to protect from the elements. Lag bolts are used to secure the underlayment.


Let’s say you own a brick mid-century modern home. It would be helpful if you added a deck to the house to increase its value. A builder can attach the deck to the masonry using lag bolts. Both short and long versions of lag shields are available.

This short version is for dense and hard bricks, while the longer version is for bricks that are less dense and softer. Long lag shields allow for deeper embedding within bricks, resulting in stronger holding values.

What Are The Different Sizes Of Lag Bolts?

Large, coarse threads appear on lag bolts (10 threads per inch for a 1/4″ bolt, dwindling to a mere 3 1/4 threads per inch for a 1 1/4″ bolt); right-handed threading is standard. Full threads are used on short lengths. For longer bolt lengths, the minimum threaded length is one-half the bolt length plus 1/2″, or 6″.

Gimlet points are threaded cone points with a point angle of 45 to 50 degrees that are used to thread into the wood. In most cases, lag bolts range between 1/4″ and 3/4″, and their lengths range from 1″ to 16″. According to the ASME standard, 7/16″ bolts are specified, but this is a size that is rarely used. Measure the length of the bolt from under the head to the threaded end.

Lag bolts come in a range of sizes. Externally wrenched bolts require adequate clearance around the head of the bolt:

Lag Bolt Size Information

Head Width

Nominal Size

Across FlatsAcross CornersHead Height



Threads Per Inch




0.2500 1/410 7/16 1/2 11/64
0.3125 5/169 1/2 9/16 7/32
0.3750 3/87 9/16 41/64 1/4
0.4375 7/167 5/8 45/64 19/64
0.5000 1/26 3/4 27/32 11/32
0.6250 5/85 15/161 1/16 27/64
0.7500 3/44 1/21 1/81 17/64 1/2

How To Select The Right Lag Bolt

Measure the width of the pieces after combining them. Ensure that the lag bolt is 1/4 inch shorter than the combined width of the two pieces.

Typically, 5/16-inch diameter lag bolts are used. If you are working on larger and heavier joints, you can use a lag bolt that is 3/8 inch in diameter.

Strength Needed

Building any kind of structure requires the proper security of all parts. To attach heavy wood structures, lag bolts are preferred over other bolts due to their strength.

Type Of Work

Strengthen your construction with these when you need them. Decks and rafter constructions use them mostly. Garages, outbuildings, etc., will also fall under this category. Thus, reading the instructions is just as important as building something!

Common Types Of Lag Bolts

  • [b]Lag bolts and lag screws with zinc plating: [/b]Moderately resistant to corrosion.
  • [b]Lag bolts and screws made of stainless steel 18-8: [/b]The corrosion-resistant properties of stainless steel make this a popular choice for exterior and marine applications.
  • [b]Silicon bronze lag bolts/lag screws: Used in wood boat building, this alloy of copper is much stronger and more corrosion resistant than brass.[/b]
  • [b]Hot-dipped galvanized lag bolts/lag screws are much more corrosion-resistant than zinc-plated ones.[/b] In coastal areas, these thick-coated lag bolts with galvanized butts are ideal for exterior use.

Related Questions

Do lag bolts need washers?

Lag bolts do not require nuts to be installed … The washer increases the contact area between the screw and the wood for screws and bolts alike. Hex heads with this feature won’t be ripped into the wood and will hold better.

Why are lag bolts stronger?

Lag screws provide higher performance due to their longer and thicker design. In spite of the pressure of heavy objects, their durable and strong properties will hold them in place.

What size pilot hole should I drill?

The general rule of thumb: a pilot or tapped hole should have the same diameter as the screw’s root (the central core just below the threads). A screw can be inserted into a board without tearing the grain yet still pulling two boards together to form a joint without tearing the grain.

Our Takeaway

There are many different types of lag bolts to choose from when it comes to your construction project. Therefore, it’s important to remember the stronger bolt you need, the smaller you should go in size. After all, the smaller bolts are the strongest. For instance, a 1/2 inch lag bolt can hold over 20,000 pounds! We were surprised too!

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Heather Robbins
Heather Robbins

Heather is a passionate writer who loves anything DIY. Growing up, she learned everything from home repairs to design, and wants to share her tips with you. When she's not writing, she's usually hiking or searching for her next DIY project.

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