Kiln-Dried vs. Air-Dried Lumber—Know Before Purchasing

Every good woodworking project starts with properly dried wood that won’t cause moisture problems later.

Unless you want picking out wood to be a guessing game, and a risk to your project, buy wood that’s been properly dried to the right moisture content. For lumber used in furniture, cabinetry, and millwork, that’s usually 6% to 8%.

How do you know whether wood is at the right moisture content?

Simple: use an accurate moisture meter from a quality manufacturer to measure the moisture content (MC) while you’re shopping. This saves time and money, because you won’t have to dry the wood yourself, which can be slow or expensive.

But what if you end up with wood that may be too wet, or you’re simply curious about different drying methods?

This article covers:

• Why the moisture level of wood is important to consider
• The differences between kiln-dried and air-dried lumber and why you ought to know

Let’s start with moisture content and why it matters.

Why is the moisture level of wood important?

Wood is a hygroscopic material.

That means it absorbs or releases moisture depending on its environment, and it swells or shrinks as it does.

All wood will change slightly with the seasons and with changes in humidity. But if you buy wood that hasn’t been properly dried, you risk much bigger changes.

Freshly sawn, or green, wood can have a moisture content anywhere from about 30% to more than 200%, depending on the species. Wood shrinkage generally doesn’t begin until the wood dries to around 28% to 30% MC, a point known as the fiber saturation point (FSP). At the FSP, the free water in the cell cavities is gone, and only the bound water in the cell walls remains. It’s the loss of that bound water from the cell walls that causes shrinkage.

So if you build something from wood that’s well above its target moisture content, it will gradually shrink, which can change its appearance and, in some cases, its safety or function.

Shrinkage problems can include warping or twisting, loose joints, splitting, adhesive failures, and other issues that take away from both the beauty and the integrity of your project.

The best way to avoid these issues is to check the wood’s moisture content with an accurate, quality moisture meter. Choose a meter from an experienced manufacturer that offers solid technical support after the sale, so you can be confident the wood has been dried to the right MC.

So what is the right MC?

What is a good moisture reading for wood?

It depends on the type of project and where it will be used.

As mentioned above, lumber for indoor furniture, cabinetry, and millwork is usually dried to 6% to 8%. In most of the U.S., the USDA Forest Service’s Wood Handbook recommends an average of about 8% for interior woodwork and furniture, with somewhat lower values in the dry Southwest and higher values in damp coastal areas.

For hardwood flooring, 6% to 9% is generally acceptable.

For outdoor projects, 9% to 14% is a good goal.

But a more reliable way to find the ideal moisture reading for your project is to consider the equilibrium moisture content of its final location.

That’s because wood left long enough in a particular temperature and relative humidity will equalize its moisture content to that environment. For example, wood kept at 35% relative humidity and about 70°F will eventually reach about 7% moisture content.

Keep in mind that equilibrium moisture content (EMC) varies by region. Outdoors, the average EMC in Miami runs about 12% to 14% through the year, while in Phoenix it ranges from about 4% to 9%.

These outdoor numbers may matter less if the project will be indoors, but they do make a difference when wood is transported or worked on in an unconditioned space.

Knowing the EMC and your target MC is one thing. Applying them when you buy wood is another, which is why it’s important to know how to measure moisture in wood.

How do you measure moisture in wood?

The best way to measure the MC of a piece of wood is with a high-quality moisture meter.

There are two basic types of moisture meters, pin and pinless, and each is more useful in some situations than others.

A pin meter leaves small holes in the wood, which may not matter for some projects.

For most woodworking projects, though, the most convenient choice is an accurate pinless moisture meter. High-quality pinless moisture meters are fast, reliable, nondestructive, and easy to use.

Look for moisture meter brands with a long, proven history of use by quality-control staff in wood products plants, such as window, door, and millwork manufacturers with strict moisture standards.

Use your pinless moisture meter to scan the lumber and check its MC, so you can walk away with wood that’s at the right MC for your project.

Now let’s talk about the drying methods used to get wood to the right MC.

Air-dried vs. kiln-dried wood

There are two primary ways to dry wood: air drying and kiln drying.

Air drying is what it sounds like: letting the wood dry naturally in the open air.

The boards are usually stacked with spacers (stickers) between the layers. Air drying is slow, and how slow depends on the species, thickness, location, and time of year. For 1-inch lumber, the Wood Handbook gives examples ranging from 15 to 30 days for some low-density species in favorable conditions to 200 to 300 days for slow-drying species like oak in northern locations. Air drying also has a limit: commercial air-dried lumber is generally around 15% to 25% MC, well above the 6% to 8% needed for indoor projects.

Kiln drying, on the other hand, dries wood in a kiln, where temperature, humidity, and air circulation are controlled.

A typical hardwood kiln schedule might start around 120°F and high humidity when the lumber is green and rise to about 180°F as the wood dries. Because conditions are controlled, a kiln dries wood much faster than air drying and can bring it down to the lower moisture content range that air drying alone can’t reach.

Careful control of temperature, humidity, and air circulation keeps a properly run kiln from damaging the wood. At the end of drying, many kilns also condition the lumber with steam or water spray, which relieves the stresses that build up during drying.

If you’re drying wood yourself, air drying may seem like the cheaper option. But it takes so long, and stops at such a high MC, that it’s usually impractical unless you plan far ahead and finish the drying indoors.

Advantages of using kiln-dried wood

There are solid reasons to choose kiln-dried wood when you buy wood for a project.

First, the heat of kiln drying typically kills insects and fungi living in the wood. That means you’re less likely to bring pests into your shop, and it helps keep wood pests and diseases from spreading to new areas when lumber is shipped.

Properly kiln-dried lumber also has a more consistent moisture content and, depending on your moisture meter readings, can often be used right away, saving you time when you start a project.

Because kiln-dried wood is generally much closer to your target moisture content, it’s less likely to shrink after you buy it, so you can move forward with less worry about warping.

Finally, kiln-dried wood may be more cost-effective than air-dried wood. Air-dried wood may cost less upfront, but drying wet wood yourself takes a lot of time, effort, and energy, and you may not be able to reach your target moisture content if the wood is stacked outside.

For most projects, kiln-dried lumber is the better investment.

Moral of the story: Buy kiln-dried and use a moisture meter

Knowing how wood is dried makes you a smarter buyer when you’re preparing for a woodworking project, and it helps you choose wood that won’t cause you grief down the line.

But no matter what wood you buy, whether it’s wet, air-dried, or kiln-dried, use a quality moisture meter so no part of the process is a guessing game. If you can accurately measure the MC of your wood, you’re setting yourself up for success.

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Last updated on October 8th, 2026