Wood Drying Time Calculator for green lumber. Pick the species, city, thickness, stacking month and method to see the days to your target moisture and which month dries it fastest.
Pick the city closest to your drying stack; its outdoor EMC sets how dry air drying can get.
Units and Starting Moisture
Fresh-sawn lumber starts at the species' green moisture from FPL averages. Use a meter reading if you have one.
Every Stacking Month
| Stack | Air | + Kiln | Air Ready |
|---|---|---|---|
| Jan | 127 | 52 | Early May |
| Feb | 122 | 51 | Early Jun |
| Mar | 114 | 48 | Late Jun |
| Apr | 105 | 45 | Mid Jul |
| May | 97 | 43 | Early Aug |
| Jun | 100 | 44 | Early Sep |
| Jul | 98 | 44 | Early Oct |
| Aug | 102 | 47 | Mid Nov |
| Sep | 165 | 70 | Mid Feb +1 yr |
| Oct | 153 | 66 | Early Mar +1 yr |
| Nov | 144 | 63 | Late Mar +1 yr |
| Dec | 146 | 59 | Late Apr +1 yr |
Air-only rows stop at your target, or half a point above the lowest monthly EMC the stack meets while drying if that is higher. Month effect follows FPL Table 9 for 4/4 red oak in Madison, WI.
Every Method Compared
| Method | Days | Ends At |
|---|---|---|
| Air Dry Only | 105 | 12.9% |
| Air Dry, Then Kiln | 45 | 8% |
| Kiln From Green | 25 | 8% |
Kiln rows use a safe drying rate for red oak of 3.0% MC per day at this thickness, plus 3 days to equalize and condition. The air stage hands off at 25% MC.
Wood Drying Time Calculator for Air and Kiln Drying
Fresh-sawn lumber can take anywhere from a few weeks to well over a year to dry, and the season it goes on stickers often matters more than the species. The Wood Drying Time Calculator estimates how long a stack will take to reach your target moisture, using Forest Products Laboratory drying data and the outdoor humidity where you live. It is built for small sawyers, woodworkers drying their own logs and anyone planning kiln time.
Pick the species, the nearest of 49 US cities, the board thickness, the month you stack and the drying method. Then set the target moisture, 8% for furniture in a heated home or 19% for dry softwood framing. The starting moisture fills in with the species' green average and can be replaced with a meter reading.
Why One Year per Inch Is Wrong
The old rule says air drying takes a year per inch of thickness. Gene Wengert, the technical advisor on the WOODWEB forum, has said that rule is not even close to the truth. He puts 1 inch lumber in warm weather at about 60 days.
The Forest Products Laboratory guide Air Drying of Lumber gives 70 to 200 days for 1 inch northern red oak to reach 20% moisture. The short end is lumber stacked in good summer weather, and the long end is lumber that sits through a winter.
Thickness also matters more than a straight line would suggest. The same FPL guide gives a rule of thumb that drying time grows with thickness raised to the 1.5 power, so 2 inch lumber takes about three times as long as 1 inch.
Real curves can be steeper still. University of Missouri Extension, reading from FPL drying curves for Columbia, Missouri, puts 4/4 red oak stacked on August 1 at 60 days to reach 20%, while 8/4 lumber stacked the same day needs almost 320.
The Month You Stack Matters Most
FPL's Table 9 shows it clearly for 1 inch red oak in Madison, Wisconsin. Stacked in May, it reaches 20% moisture in about 65 days. Stacked in September, it takes about 212, because the drying stalls through the winter.
The Air Drying of Lumber guide says lumber piled in fall or winter usually does not reach 20% until the following spring. The tool applies that seasonal pattern to every species and region, and the Every Stacking Month table lists the air-only and air-plus-kiln time for all twelve months.
With the defaults, 4/4 red oak in St. Louis stacked in April needs 45 days with a kiln finish. Stacked in September, the same boards take 70 days, since the air stage runs into cold weather before the stack reaches the kiln.
Outdoor Air Sets a Floor
Air-dried wood can only get as dry as the outdoor air allows. That limit is the equilibrium moisture content, and FPL's Table 3 lists it by month for 49 US cities. The tool uses that table for the city you pick.
St. Louis ranges from 12.4% in April to 14.9% in December and averages 13.5%. Phoenix drops to 4.6% in June, while Seattle never goes below 12.2%. Oregon State University Extension says air-dried wood in western Oregon settles at 12% to 14%, against 8% to 10% east of the Cascades.
Air Dry Only stops at your target or half a point above the lowest monthly EMC the stack meets while drying, whichever is higher. The default red oak ends near 12.9% after 105 days. Reaching 6% to 8% for indoor furniture takes a kiln or a heated shop.
For outdoor work the floor is not a problem. The FPL guide says air drying is usually enough for outdoor furniture and for unheated buildings such as barns and garages.
Air Dry First, Then Kiln
FPL notes that mills drying slow species such as oak usually air dry first and kiln dry after. Air-dried lumber usually stays on stickers until it reaches 20% to 25%, and the tool hands off to the kiln at 25%.
Kiln time depends on how fast each species can lose moisture without checking. A Woodworking Network column on kiln drying oak puts the maximum for 4/4 red oak at 3.8% moisture loss per day, averaging about 3.0%. For white oak the figures are 2.5% and about 2.0%.
The OSU Extension air drying guide lists Wengert's maximum rates for other 4/4 hardwoods. Hard maple is 6.5%, cherry 5.8%, walnut 8.2% and soft maple 13.8% per day.
M1 and M2 are the starting and ending moisture, r is the average daily rate and the 3 days cover equalizing and conditioning. At 3.0% a day, red oak from 25% to 8% takes about 6 days plus conditioning.
OSU Extension says green 4/4 white oak can take more than a month in a kiln, while air-dried white oak takes one to two weeks. The tool gives 32 days from green and about 12 in the kiln after air drying. Softwoods are kiln dried on time-based schedules, so for those the tool models air drying only.
What Happens at 30% and 20% Moisture
The second card splits the drying into stages. Above about 30%, the fiber saturation point, free water leaves the cell cavities and the wood does not shrink. Below it, the cell walls dry and the board starts shrinking.
At 20% or less, blue stain and wood-destroying fungi can no longer grow, according to FPL. The default red oak reaches 30% in about 26 days, 20% about 12 days later and the 8% target a week after that.
To see how much the boards will shrink between those stages, use the Green Wood Shrinkage Calculator. For how much lighter the stack gets as it dries, the Wood Weight Calculator works at any moisture content.
Checking the Stack Is Really Dry
How do I know when lumber is dry enough to use?
Measure it rather than trusting the calendar. FPL's air drying guide says pin meters are reasonably accurate from 7% to 25% moisture, as long as the pins reach a fifth to a quarter of the board's thickness.
Check several boards, including some from the lower courses, which FPL notes dry more slowly than the top of the pile. For the most reliable reading, OSU Extension describes weighing a sample board, oven drying slices cut from it, and reweighing the board to track its moisture over time.