How Long to Dry Lumber: Air-Drying Times by Species

The short answer: green 1 in (4/4) lumber stacked outdoors in good drying weather reaches about 20% moisture content in anything from about 2 weeks to about 4 months, depending on the species, according to the US Forest Products Laboratory. Light woods such as pines, spruces, basswood and soft maples are at the fast end; oaks and beech are slow, and tanoak takes about 6 months. Lumber stacked in the fall usually will not reach 20% until the following spring. Thicker boards take much longer: 2 in (8/4) stock needs about three times as long as 1 in. And air drying stops at the moisture content of the outdoor air, about 6% to 16% on average across 49 US cities, so wood for furniture and floors has to finish drying indoors or in a kiln.

The old rule of “one year per inch” is a rough rule for hobby stacks. The figures below are the USDA’s, from Air Drying of Lumber (FPL-GTR-117), and they explain where that rule comes from and when it is too slow or too fast.

Air-drying time by species: 1 in lumber to 20% moisture content

1 in vs 2 in hardwood lumber, by region

For eastern hardwoods the report gives drying times in four regions of the eastern United States, from the South to the Mid-North (its Figure 23 maps them). The 2 in figures show how fast drying time grows with thickness: the 2 in boards take three to four times as long as the 1 in boards in the same region.

Thicker boards: the 1.5 power rule

The report gives a rule of thumb: drying time grows with the thickness raised to the power 1.5. A board twice as thick takes about 2.8 times as long, not twice as long, because the water has twice as far to travel and the surface is no larger. Applied to a species that takes 70 to 200 days at 1 in, such as northern red oak, black cherry or black walnut:

This is where “a year per inch” comes from: a 1 in board stacked in the fall and a 2 in board stacked in good weather can both take roughly a year to reach 20%. For 8/4 oak the report’s own figures are 190 to 360 days.

How dry can air-dried lumber get?

Air-dried wood only gets as dry as the air it sits in. Outdoors, its equilibrium moisture content (EMC) averages 6.2% in Las Vegas, NV (the driest of the 49 cities in Wood Handbook Table 13-1) and 16.0% in Juneau, AK (the dampest), with a median of 13.1%. For indoor work the Wood Handbook (Table 13-2) recommends an average of 8% for interior woodwork, flooring and furniture in most of the United States (individual pieces 6% to 10%), 6% in the dry Southwest and 11% in damp, warm coastal areas. Exterior siding and trim should be about 12% (9% in the dry Southwest).

So air drying gets furniture wood to roughly 12% to 15% in most places. Bring it inside, stickered, into a heated room for several weeks (or have it kiln dried) and check it with a moisture meter before you build. Wood worked at 12% and then brought into a heated house in winter will shrink, and panels, joints and tabletops can open up or split; see the wood shrinkage chart for how much.

How to stack lumber to air dry

• Get it on stickers quickly. Freshly sawn lumber left in a solid pile stains and grows mold within days in warm weather. The report repeatedly stresses stacking promptly and getting good air movement.
• Raise the stack. Keep the bottom layer well off the ground on a firm, level foundation; the report gives 8 in (200 mm) as the minimum foundation height in forklift yards and wants free air movement underneath. A level base matters: the stack takes the shape of its foundation, and boards dry into that shape.
• Use dry, uniform stickers. Stickers should be dry (wet ones leave stained sticker marks), straight and all the same thickness. Hardwood stacks commonly have stickers 16 in to 2 ft apart; five stickers are usual on 16 ft softwood boards and five to nine on 16 ft hardwood boards. Line them up vertically, one above the other.
• Coat the ends. Coat freshly trimmed ends of valuable lumber thicker than 1-1/4 in with an end coating (wax emulsion or a commercial end sealer) to limit end checks and splits.
• Roof it, but let it breathe. A rain-tight roof or cover keeps rain and sun off the top layers; leave the sides open. Weight the top to reduce warp.
• Pick the spot. High, open, dry ground with good wind dries fastest; valleys and sites surrounded by trees or buildings dry slowly and encourage mold and stain.

When is it dry? Checking and storing

Moisture meters are quick and good enough for woodworking. For a more accurate figure, weigh a sample board cut from the stack (with fresh end-sealed ends) every week or two; when the weight stops falling, the board has reached the outdoor EMC. Once lumber is at 20% or below, the report says it can be bulk piled without stickers if it is protected from rain; wetter lumber should stay on sticks. Indoors, keep it stickered and give it air movement until it reaches the room’s moisture content.

Common problems

• Surface checks in oak and beech: drying too fast in hot, windy weather; shade the stack or slow the air.
• End checks and splits: no end coating, or ends overhanging the last sticker.
• Blue stain and mold: slow drying in warm, humid weather, or boards left unstickered; sapwood is most prone, especially in pines.
• Sticker stain: wet or green stickers.
• Warp (bow, cup, twist): uneven foundations, stickers out of line or too far apart, and no weight on top.

Frequently asked questions

How long does it take to dry lumber after it is milled?

For 1 in boards stacked outdoors in spring or summer, from about 2 weeks (some pines and Douglas-fir) to about 4 months (southern oaks) to reach 20% moisture content (USDA FPL-GTR-117, Table 7). Stacked in fall or winter, expect to wait until the next spring. Then allow several weeks indoors to reach furniture moisture content.

How long does 2 in (8/4) lumber take to air dry?

About three times as long as 1 in. The USDA figures for eastern hardwoods are mostly 170 to 250 days for 2 in stock, and 190 to 360 days for 2 in oak.

Is "one year per inch" right?

As a rough planning figure for a hobby stack, it is on the safe side for 1 in lumber of most species and about right for 2 in hardwoods. Drying time grows faster than thickness, roughly with thickness to the power 1.5, so very thick stock takes more than a year per inch.

Can you air dry lumber in winter?

It dries very slowly in cold weather. The USDA notes that lumber stacked in fall or winter usually does not reach 20% moisture content until the following spring, though stacking it in winter still lets it start drying without staining.

Can air-dried lumber be used for furniture?

Only after it has dried further indoors. Outdoor air holds wood at about 6% to 16% moisture content on average, against about 8% recommended for interior woodwork in most of the US.

Sources

1. Forest Products Laboratory. 1999. Air Drying of Lumber. General Technical Report FPL-GTR-117. USDA Forest Service, Madison, WI: Table 7, Table 8, drying-time and thickness text, sticker spacing, foundations, end coating, storage. A US Government work.
2. USDA Forest Products Laboratory, Wood Handbook FPL-GTR-190 (2010): Table 13-1 (outdoor equilibrium moisture content, 49 US cities), Table 13-2 (recommended moisture content at installation).

Last reviewed: 25 October 2026. Related: wood species database, wood shrinkage chart, equilibrium moisture content calculator, wood movement calculator. Spotted an error? Please let us know.