Tree Portion Calculator: Estimate Tree Size

A tree portion calculator estimates the size of a tree section—such as the volume of a log, the weight of a branch, or the area of a canopy—based on measurements you take from the tree itself. You enter dimensions like diameter, length, and height, and the calculator returns an estimate of volume, weight, or surface area using standard geometric formulas. This tool helps with planning removals, estimating firewood, or assessing habitat value without cutting the tree down.

Formula

The calculator uses the formula for the volume of a cylinder, adjusted for bark thickness and taper:

V = π × ((D/2 − T) / 12)² × H

• V = volume of the trunk inside bark (cubic feet)
• D = diameter at breast height (inches), measured 4.5 feet above ground
• T = bark thickness (inches)
• H = merchantable height (feet), the usable length of the trunk

The division by 12 converts inches to feet so that volume comes out in cubic feet. The weight estimate uses an average green wood density of 55 pounds per cubic foot, which varies by species and moisture content.

Worked Example

Using the default values from the calculator:

• DBH = 18 inches
• Merchantable height = 30 feet
• Bark thickness = 1 inch

First, subtract bark thickness from the radius: (18/2 − 1) = 8 inches. Convert to feet: 8/12 = 0.6667 feet. Square that: 0.6667² = 0.4444. Multiply by π: 0.4444 × 3.14159 = 1.3963. Multiply by height: 1.3963 × 30 = 41.89 cubic feet. The calculator rounds to 41.89 ft³. For weight: 41.89 × 55 = 2304 pounds (rounded). Firewood cords: 41.89 / 128 = 0.33 cords.

When to Use a Tree Portion Calculator

This tool is useful for several practical situations:

• Estimating how much firewood a fallen tree will produce
• Planning a tree removal and estimating disposal costs
• Assessing the biomass of a branch or trunk for habitat or composting
• Comparing the size of different trees for landscaping decisions

It is not a substitute for professional tree risk assessment. A certified arborist uses more detailed methods to evaluate structural integrity, disease, and root health.

How to Measure Tree Portions

Accurate measurements are key to a good estimate. Follow these steps:

1. Measure DBH at 4.5 feet above ground on the uphill side of the tree.
2. For a log, measure the diameter at the small end (inside bark) and the length.
3. For a branch, measure the base diameter and the length along the centerline.
4. Bark thickness varies by species; use a bark gauge or estimate from a nearby cut surface.

If measuring a standing tree, use a diameter tape or a regular tape measure and divide by π (3.14) to get diameter from circumference.

Common Mistakes and Limitations

One common mistake is using the diameter at the large end of a log instead of the small end. The formula assumes a cylinder, but real logs taper. For more accuracy, use the small-end diameter, which gives a conservative estimate. Another error is forgetting to subtract bark thickness when measuring outside bark. The calculator subtracts it once, but if you measure inside bark, set bark thickness to 0.

The formula also assumes a straight, uniform trunk. Trees with significant taper, buttresses, or irregular shapes will produce estimates that differ from actual volume. For firewood, the stacked volume (cord) includes air spaces, so the calculator’s cord estimate assumes a solid cylinder—actual stacked cords will be larger.

Comparing to Alternative Methods

There are more precise ways to measure tree volume, such as the Smalian’s formula, which uses both end diameters, or using a laser rangefinder and a clinometer for standing trees. These require more equipment and calculation. The cylinder formula here is a good balance between simplicity and accuracy for most casual uses.

For weight, the density varies widely: oak is about 50–60 lb/ft³ green, while pine is 30–40 lb/ft³. If you know the species, adjust the density in the calculator accordingly. The default of 55 lb/ft³ is a reasonable average for mixed hardwoods.

Cost and Safety Considerations

Using a tree portion calculator is free and requires no special training. However, measuring a standing tree often requires climbing or using a pole to reach heights, which carries fall risks. Always use proper safety gear and consider hiring a professional for large trees. For felled trees, be aware of chainsaw safety and the weight of the logs—a 2-foot diameter oak log can weigh over 2,000 pounds.

Frequently Asked Questions

How accurate is a tree portion calculator?

Accuracy depends on how well the tree matches a cylinder shape. For a straight, uniform trunk, the estimate can be within 10–20% of actual volume. Tapered or irregular trees will have larger errors.

What is the difference between a cord and a cubic foot?

A cord is a stacked volume of wood measuring 4 × 4 × 8 feet, equal to 128 cubic feet of space including air gaps. A cubic foot is a solid volume. The calculator converts solid volume to cords by dividing by 128, but actual stacked cords will be larger because of air spaces.

Can I use this for a branch or just the trunk?

Yes, you can use the same formula for a branch if you measure its base diameter and length. Treat the branch as a cylinder, but note that branches taper more than trunks, so the estimate will be less accurate.

How do I measure diameter if I only have a circumference tape?

Divide the circumference by π (3.14) to get the diameter. For example, a circumference of 56.5 inches divided by 3.14 gives a diameter of 18 inches.

Does the calculator work for all tree species?

The volume formula works for any species, but the weight estimate uses an average density. For species like balsa (very light) or ironwood (very heavy), the weight will be off. Adjust the density factor if you know the species.

What if the tree has a large buttress or flared base?

Measure DBH above the flare, typically at 4.5 feet, which is standard practice. The formula will still give a reasonable estimate for the merchantable portion above that point.

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in d | Trunk diameter at breast height (DBH) | in | 18 | 0
in h | Merchantable height (usable log length) | ft | 30 | 0
in t | Bark thickness | in | 1 | 0
out vol | Trunk volume (inside bark) | ft³ | (pi * ((d/2 - t)/12)^2 * h) | 2
out weight | Estimated green weight | lb | vol * 55 | 0
out cords | Firewood cords (stacked) | cords | vol / 128 | 2