How foresters calculate the volume of timber in your woods
If you’ve ever wondered how much timber is standing on your land, you’re not alone. Many Ohio landowners are surprised to learn just how valuable their woods can be –when measured correctly. The process foresters use to estimate the total volume of merchantable timber on your property is part science, part math, and part fieldwork.
Here’s a clear breakdown of how it works.
Foresters don’t need to measure every tree - they sample instead
It would be impractical to measure every tree on any wooded property larger than 20 acres. Instead, professional foresters use statistical sampling methods to take representative measurements and apply them to the whole stand.
This approach relies on:
- Plot sampling: measuring trees in specific locations
- Volume equations: translating those measurements into board feet
- Extrapolation: projecting total volume across the entire property.
When done correctly, this gives a reliable estimate of the total board footage — and therefore the market value — of your timber.
Step one: laying out sample plots
Foresters begin by walking your woods and laying out sample plots. These plots might be:
- Fixed-area plots – usually circular plots of a known size (like 1/10-acre)
- Variable-radius plots – using a tool like a prism or angle gauge to count trees based on size and distance
Variable-radius plots are faster and more commonly used in timber cruising. This method depends on something called the Basal Area Factor.
Step two: understanding the basal area factor (BAF)
Basal area is the cross-sectional area of a tree trunk measured at 4.5 feet above the ground — also known as diameter at breast height (DBH).
Instead of calculating each tree’s basal area manually, foresters use a Basal Area Factor (BAF) with a prism or angle gauge to determine how much timber is in a given area.
Here’s how it works:
- The forester stands at a plot center and uses a wedge prism or angle gauge to spin 360°
- Each tree that appears “in” based on the viewing angle and its diameter, is counted
- Each “in” tree represents a certain number of square feet of basal area per acre — that’s the BAF
Example:
- BAF = 10
- You count 7 “in” trees at a plot
- That plot represents 70 ft² of basal area per acre
This number, combined with average tree height and species, allows the forester to estimate total timber volume.
Step three: calculating board feet
Once basal area is known, the forester uses volume equations (based on species, DBH, and merchantable height) to calculate board feet per tree.
The log rules used in Ohio are:
- Doyle Rule
- International ¼-Inch Rule
- Scribner Rule (rarely)
These formulas help estimate how many board feet can be harvested from each tree or plot. That value is then scaled up to reflect the full acreage.
Example:
- Each acre is estimated to contain 8,500 board feet
- Your woods are 42 acres
- Total volume: 357,000 board feet
Step four: verifying accuracy
Professional foresters typically cruise enough plots to keep the sampling error low. They may also calculate a confidence interval to show how precise the estimate is. If you’re selling timber, this matters –an accurate estimate gives you leverage when comparing bids.
When he’s preparing a stand for sale, however, a forester will count every board foot in every tree to be sold.
The result: a detailed timber inventory
Once the sampling and calculations are complete, the forester will prepare a report breaking down:
- Estimated board feet by species
- Grade (e.g., sawtimber, veneer, blocking)
- Total volume per acre and per stand
- Estimated market value
This inventory becomes the basis for timber marketing, competitive bidding, and long-term management planning.
Final thoughts
If you’re thinking about selling timber, don’t let a logger or timber buyer determine the value in your woods. That’s how landowners get shortchanged. A professional timber cruise, conducted by a certified forester using proper statistical sampling, is the only reliable way to know what your timber is truly worth.
- Minimum: 10 wooded acres or 50 mature trees.