Screw and nail holding strength
How hard a fastener is to pull straight back out, by what it is in and how deep it goes. The big number is after a safety factor — the ultimate figures beside it are laboratory loads, not loads to build to.
5 is the common divisor for a static load
Safe to build to
252lb
All 4 at ultimate
1,262 lb
One fastener, ultimate
315 lb
Per inch of depth
315 lb
Read the big number, not the ultimate
The ultimate figures are what a fastener tore out at in a laboratory test on clear, conditioned wood. They are not loads to design to. Dividing by 5 is what makes the number above usable, and a sustained load, a shared load or anything over somebody's head wants more than that.
This is withdrawal from side grain only. End grain holds around three quarters of it at best and unreliably enough that the Wood Handbook advises not designing for it at all. Nothing here predicts the fastener itself snapping, or the wood splitting, and nothing here governs a structural connection — that is the NDS, the hardware manufacturer, and an engineer.
The same wood screw, one inch deep, in every wood
- Walnutspecific gravity 0.55
- 779 lb
- White oakspecific gravity 0.68
- 1,191 lb
- Red oakspecific gravity 0.63
- 1,022 lb
- Hard maplespecific gravity 0.63
- 1,022 lb
- Soft maplespecific gravity 0.54
- 751 lb
- Cherryspecific gravity 0.5
- 644 lb
- Poplarspecific gravity 0.42
- 454 lb
- Ashspecific gravity 0.6
- 927 lb
- Hickoryspecific gravity 0.72
- 1,335 lb
- Mahoganyspecific gravity 0.5
- 644 lb
- Sapelespecific gravity 0.62
- 990 lb
- White pinespecific gravity 0.35
- 315 lb
- Douglas firspecific gravity 0.48
- 593 lb
- Cedarspecific gravity 0.32
- 264 lb
Ultimate load per inch, so the spread is the whole point: holding power rises with the square of specific gravity for a screw, which is why the wood matters more than the screw. These are Wood Handbook species averages — a good bet across a stack of boards and no promise about the one in your hand.
Why the numbers look like this
Holds on the square of the wood's density. The smooth shank under the head does no work, so only the threaded length in the receiving board counts.
From the USDA Wood Handbook's withdrawal equations: 15,700·G²·D for a wood screw, 7,850·G^2.5·D for a nail and 7,450·G^1.5·D^0.75 for a lag, in pounds per inch of penetration.
About fastener holding power
- How much weight can a screw hold?
- Far less than the number a test machine gets, and that gap is the most important thing on this page. The USDA Wood Handbook's equation for a wood screw is 15,700 × G² × D pounds per inch of thread, where G is the wood's specific gravity and D the shank diameter — a #10 screw with an inch of thread in red oak comes out near 1,200 lb. That is the load at which it tore out of a clear, conditioned test specimen. Divide by five for something to actually build to, and more if the load is sustained or overhead.
- Why does the species matter so much?
- Because holding power goes up with the square of the wood's density, not in step with it. Twice the specific gravity is four times the withdrawal. That #10 screw pulls about 365 lb per inch of thread out of eastern white pine and about 1,550 out of hickory — more than four times as much, from the same screw — and no amount of picking a better fastener closes a gap that big. If a joint is marginal, the wood it lands in is the biggest lever you have.
- Is a fatter screw or a longer one better?
- Longer, almost always. Withdrawal is linear in diameter and linear in penetration, so the two look equal — but you can usually double the thread depth and you can rarely double the gauge without splitting something. A lag is even more one-sided: its diameter term is D^0.75, so going up a size buys less than proportionally while depth still pays in full.
- What about screwing into end grain?
- Do not design for it. End-grain withdrawal runs at roughly three quarters of the side-grain figure at best and is unreliable enough that the Wood Handbook advises against counting on it. These equations are for side grain only, and there is no coefficient here that makes an end-grain screw safe — if a joint has to pull against end grain, it wants a different joint, a threaded insert, or a cross dowel.
- Can I use this for a structural connection?
- No. This is laboratory ultimate load from a published equation about wood, and a real connection is governed by the NDS, the fastener manufacturer's own rated capacity, and the code — plus failure modes this says nothing about, like the screw itself snapping or the wood splitting. Treat it as a way to compare options and to sanity-check a shop joint, and get anything holding a structure up on paper from somebody who will stamp it.
You might also need
- Screw lengthHow long a screw to put through one board into another, and whether the tip comes out the far side.
- Pilot hole calculatorThe right drill bit for a wood screw, by gauge number and by softwood or hardwood.
- Bolt and lag spacingEdge, end and row distances for bolts through a timber, in the multiples of diameter the NDS sets.
- Shelf sag and spanHow far a shelf bends under books, how far it can span, and what a strip on the front edge buys you.