If you’re attaching shelves to a wall, you need to pay attention to weight. How much weight can a screw in a stud hold? And is there any way to increase the amount of weight it can hold?
A screw in a stud can generally hold 80-100 pounds, depending on the grade of screw. There are tricks to increase the amount of weight it can hold.
How to increase how much weight a screw in a stud can hold
The easiest way to increase the amount of weight a screw in a stud can hold is to simply double up. If you have room for a second or a third screw, just add more. Two screws can hold 160-200 pounds. Three screws can hold 240-300 pounds. Here’s how to use a stud finder to find the center for best results. You can double up like this because the stud itself can hold several hundred pounds.
Distribution also helps, especially to keep the shelves from sagging. If whatever you’re hanging spans multiple studs, use each stud. This distributes the load more, and also gives you more opportunity to double up. If you’re using cleats or brackets, and they attach to the wall with more than one screw, all of the screws count.
The grade of screw matters as well. A construction screw holds more weight than a cheap drywall screw. Spending a a few dollars on a box of construction screws, even if it means buying a box rather than using drywall screws you have on hand, is a good idea if you’re hanging something heavy. It will save you time and trouble down the road. Construction screws are usually thread-cutting too, which makes putting things together much easier. You have to consider the ease of putting things together, in addition to the cost and durability.
Doing the math
Take my 8-foot span of storage shelves in my garage. With studs about 16 inches apart, an 8-foot span should have about five studs to screw into. At two screws per stud, each shelf can support 800-1,000 pounds. Realistically, I probably won’t be putting more than 200-300 pounds on each, since I designed the shelves to hold storage bins. When full, the bins rarely weigh 40 pounds each, and I can stuff about 8 bins on a shelf. The shelves themselves probably weigh about 30 pounds.
These shelves have legs on the front of the shelves too, and those count. I only put three legs on the front, but that’s six more screws, for an additional 480-600 pounds.
I guess I’m saying the math says my shelves are overbuilt. But there’s also a difference between smart cheap and foolish cheap. If I’m worried about 75 cents’ worth of screws in a project that cost me less than $50, that borders on foolish. The shelf also has to hold itself together as I’m assembling it, and doubling up on screws helps to hold everything straight and square during assembly. I think I’ll leave well enough alone.
These rules all hold for shelves hanging from a ceiling as well. You’ll definitely want to overbuild those, however, as you don’t want those crashing down.