How Much Weight Can a 4×4 Support Horizontally? [It Depends!]

When building a structure, you must consider the amount of weight that the lumber you are using will support. There are many factors when choosing the type of lumber to use. Lumber has different types of wood, grades, and treatments. This can make it hard to figure out the right numbers.

The amount of weight that a 4×4 can support horizontally will depend on the type of wood you are using, the grade of wood, and the length of the board itself. Your average yellow pine 4x4x8 will be able to hold up to two tons (4,000 lbs), with the correct vertical support beneath it.

These numbers are based on your average yellow pine 4×4, at 8 feet in length. The number may vary, depending on the grade of the wood, and the condition.

Each of these, are standard for construction. They are strong enough to build large structures and last over time. Yellow pine is used, in the stick framing of most houses. 4×4 southern yellow pine is strong and is available at most hardware stores. It is the most inexpensive choice, while still being a standard for construction.

The Douglas fir is another strong wood that is used in construction. It accounts for one-fourth of all lumber in the United States. Pressure-treated timber is probably the best choice if your 4×4 is exposed to the elements outdoors.

Red cedar is a good choice if you are going for a certain type of look. It is a quality wood with great density. It comes in rough and smooth. Oak is one of the harder woods. It is the strongest and will hold up better than any of the others on this list.

Lumber comes in more than one grade. This has to do with the quality of the board. There are three main grades when it comes to the best lumber for supporting weight. These are considered an industry standard.

Number 1 Grade

Number one grade is the best, for structural construction. This lumber has fewer knots and can be painted over easily.

Number 2 Grade

Number two grade wood is your standard wood, used for construction. It has more knots than the number one, and larger knots. It can also be painted over easily.

Number 3 Grade

The number three grade wood is the lumber of the least quality. It has splits and several large knotholes. If your 4×4 is meant to support a lot of weight, avoid number three grade lumber.

The lumber that is going to perform the best, when it comes to how much weight it will support, would be the number one and number two grades. When picking out your lumber, there are a few things you will want to consider. Since you will want your 4×4 to be able to support as much weight as possible, you will need to carefully choose your boards.

Look for 4×4 boards with fewer knotholes. The more knots the board has, the weaker it is going to be. You also want to make sure that the board is straight. You can do this by picking up the board from one end, tilting it downward, and looking to see that the edge is straight, and not bowed.

Bowed wood is of lesser quality and could break under too much weight.

If you are using your 4×4 horizontally, then the amount of vertical support the board has will have a lot to do with how much weight the board will support.

If you were to have it held up on each end with lumber, but no vertically support in the middle of the board, it would not hold nearly as much weight. Only a few hundred pounds.

With corner boards at each end, and vertical support every 16 inches you will obtain the 2 tons of weight, explained in this article.

The span or length of the board also comes into play here. Depending on how long your 4×4 is, having the proper vertical support, will make sure that it holds up to the weight.

What are some other options other than a 4×4?

Another option other than a 4×4 is to take two 2x4s and fasten them together with nails. It can be argued that this is stronger than a 4×4. Both the 2x4s are rated to hold one ton of weight each, nailed together they will hold two tons (4,000 lbs), with the added strength of the nails.

Is a 4×4 board the best option horizontally?

4x4s are not typically used to support weight horizontally. You would be better off using a 2×6 or 2×12 on edge. These are the standard boards, used as headers for doors and windows, in stick framing construction.