How to Calculate Board Feet in Logs: A Complete Guide

Have you ever wondered how lumber mills estimate how much usable wood they can get from a raw log? Unlike calculating board feet for standard lumber from the hardware store, estimating board feet in logs requires special scaling rules. This is because logs are irregular, tapered, and contain natural defects that affect the final lumber yield.

Whether you’re a landowner selling timber, a sawmill operator, or a woodworker sourcing raw logs, understanding log scaling is essential for accurate estimates and fair pricing. In this comprehensive guide, we’ll walk you through the three main log scaling rules used in North America and show you exactly how to measure and calculate board feet in logs.

Why Logs Need Special Scaling Rules

You might be thinking: “Why can’t I just use the standard board foot formula?” The answer lies in the fundamental differences between milled lumber and raw logs.

Standard lumber is already processed into rectangular boards with consistent dimensions. A 2×4×8 is predictable and uniform. Raw logs, on the other hand, present several challenges:

1. Irregular Shape: Logs are round (or oval) and taper from the large end (butt) to the small end (top). They’re not perfect cylinders.

2. Bark and Waste: The outer bark doesn’t count as usable lumber. Additionally, the sawing process creates waste in the form of sawdust (kerf) and unusable edge pieces (slabs).

3. Natural Defects: Knots, rot, splits, and other imperfections reduce the amount of quality lumber you can extract.

4. Sawing Efficiency: Different sawmill technologies and cutting patterns affect how much lumber you can recover from a log.

Because of these factors, specialized log scaling rules were developed over the past 200 years to provide standardized estimates. These rules account for taper, waste, and typical sawing practices to give you a realistic board foot estimate before the log is ever cut.

The Three Main Log Scaling Rules Explained

In North America, three log scaling rules dominate the industry. Each was developed at a different time and uses different assumptions about sawing efficiency and waste. Let’s explore each one in detail.

Doyle Log Rule: The Conservative Classic

Developed in 1825, the Doyle Rule is the oldest log scaling method still in use today. It was created by Edward Doyle and is particularly popular in the eastern United States.

The Doyle Formula

Board Feet = ((D - 4)² × L) / 16

Where:
D = Small-end diameter inside bark (inches)
L = Log length (feet)

How It Works

The Doyle Rule subtracts 4 inches from the diameter to account for slab waste and sawdust, then squares that value. This approach is very conservative, especially for smaller logs.

Pros and Cons

Advantages:

• ✅ Simple to calculate mentally
• ✅ Conservative estimates reduce disputes between buyers and sellers
• ✅ Widely accepted in traditional timber markets

Disadvantages:

• ❌ Severely underestimates yield for logs under 16 inches in diameter
• ❌ Doesn’t reflect modern, efficient sawmill technology
• ❌ Can result in unfair pricing for small-diameter timber

Best Used For

The Doyle Rule works best for large-diameter logs (over 16 inches) in traditional lumber markets, particularly in the eastern United States where it remains the regional standard.

Scribner Log Rule: The Industry Standard

Developed in 1846 by J.M. Scribner, this rule is based on actual diagrams of boards that could be cut from logs of various sizes. It’s the most widely used rule in the United States today.

The Scribner Formula

Board Feet = (0.79 × D² - 2 × D - 4) × (L / 16)

Where:
D = Small-end diameter inside bark (inches)
L = Log length (feet)

How It Works

Scribner drew circles representing log cross-sections and sketched in rectangular boards that could be cut from each circle. He accounted for a 1/4-inch saw kerf (the width of the saw blade cut) and edge waste. The formula is derived from these practical diagrams.

Pros and Cons

Advantages:

• ✅ Based on real-world cutting patterns
• ✅ Widely accepted across the industry
• ✅ More accurate than Doyle for a broader range of log sizes
• ✅ Balances buyer and seller interests fairly

Disadvantages:

• ❌ Still somewhat conservative for small-diameter logs
• ❌ More complex to calculate without a calculator or chart

Best Used For

Scribner is the go-to rule for general-purpose log scaling, especially for logs between 12 and 40 inches in diameter. It’s the standard in most U.S. National Forests and commercial timber sales.

International 1/4” Rule: The Most Accurate

Developed in 1917 by the U.S. Forest Products Laboratory, the International Rule is the most scientifically accurate of the three. It’s based on the geometric volume of a cylinder, minus realistic allowances for taper, saw kerf, and slabbing.

The International Formula

Board Feet = (0.905 × D² - 1.818 × D) × (L / 16)

Where:
D = Small-end diameter inside bark (inches)
L = Log length (feet)

How It Works

This rule calculates the volume of a cylinder (the log), then subtracts a fixed amount for a 1/4-inch kerf and edge waste. It assumes a slight taper and uses mathematical precision rather than hand-drawn diagrams.

Pros and Cons

Advantages:

• ✅ Most accurate across all log diameters
• ✅ Based on solid mathematical principles
• ✅ Reflects modern sawmill efficiency
• ✅ Fair for both small and large logs

Disadvantages:

• ❌ More complex formula
• ❌ Less widely adopted than Scribner in the U.S.
• ❌ May produce higher estimates than traditional buyers expect

Best Used For

The International Rule is ideal for precision estimates, export markets, and situations where you need the most accurate yield prediction. It’s commonly used in Canada and for international timber trade.

Comparing the Three Rules: Real Examples

Let’s see how these three rules compare when applied to the same logs. The differences can be significant, especially for smaller logs.

Example 1: Small-Diameter Log (12” × 16’)

Analysis: For this small log, the Doyle Rule estimates nearly half what the International Rule predicts. If you’re selling small-diameter timber using Doyle, you’re likely getting underpaid.

Example 2: Medium-Diameter Log (20” × 16’)

Analysis: The gap narrows as log diameter increases. Scribner sits comfortably in the middle, which is why it’s the most popular compromise.

Example 3: Large-Diameter Log (30” × 16’)

Analysis: For large logs, Doyle becomes more reasonable, though it still lags behind the other two rules. This is why Doyle remains popular in regions with large, old-growth timber.

How to Measure Logs for Board Feet

Accurate measurement is just as important as choosing the right scaling rule. Here’s a step-by-step guide to measuring logs correctly.

Step 1: Measure the Length

• Measure from the large end (butt) to the small end (top) in a straight line.
• Round to the nearest foot.
• Standard log lengths are 8, 10, 12, 14, or 16 feet. Longer logs may need to be divided into shorter sections.

Step 2: Measure the Small-End Diameter

This is the most critical measurement. Always measure the small end of the log, not the large end.

• Use a diameter tape or calipers to measure across the center of the small end.
• Measure the diameter inside bark (DIB), not including the bark thickness.
• Round to the nearest inch.

Why the small end? The small-end diameter represents the minimum usable diameter of the entire log. It’s the most conservative and fair measurement standard.

Step 3: Check for Defects

While the formulas don’t automatically account for defects, you should note any significant issues:

• Large knots
• Rot or decay
• Splits or cracks
• Severe crook (bend)

For logs with major defects, you may need to deduct 10-30% from the calculated board feet, or consult a professional timber cruiser.

Step 4: Divide Long Logs into Sections

If your log is longer than 16 feet, it’s often best to divide it into standard-length sections (e.g., two 16-foot logs from a 32-foot tree). Measure each section separately and add the results.

Common Measurement Mistakes to Avoid

• ❌ Measuring the large end instead of the small end – This will overestimate yield.
• ❌ Including bark thickness – Bark is not usable lumber.
• ❌ Using non-standard lengths without adjustment – Odd lengths can complicate pricing.
• ❌ Ignoring taper – Long logs with significant taper should be sectioned.

Which Log Scaling Rule Should You Use?

Choosing the right rule depends on your location, the size of your logs, and industry standards in your area. Here’s a practical decision guide.

Decision Tree

If you’re in the eastern United States and dealing with traditional timber buyers → Use Doyle
If you need an industry-standard estimate accepted nationwide → Use Scribner
If you want the most accurate estimate or are exporting timber → Use International
If your logs are under 16 inches in diameter → Use International (Doyle will severely undervalue them)
If you’re negotiating a timber sale → Know all three and understand which rule the buyer uses

Regional Preferences

• Eastern U.S.: Doyle is still common, especially in Appalachia and the South.
• Western U.S.: Scribner is the standard.
• Canada: International Rule is widely used.
• Export Markets: International Rule is preferred for consistency.

Pro Tip for Sellers

If you’re selling timber, always clarify which scaling rule will be used before agreeing on a price. A buyer using Doyle on small-diameter logs will pay significantly less than one using International, even for the same wood.

Understanding the Formulas: Key Assumptions and Limitations

All three log scaling rules are based on assumptions and simplifications. Understanding these will help you interpret the results correctly.

Common Assumptions

1. Logs are cylindrical or slightly tapered cones – Severely crooked or irregular logs won’t match the formula.
2. Small-end diameter represents the entire log – This is conservative but fair.
3. Standard saw kerf of 1/4 inch – Modern thin-kerf saws may yield slightly more.
4. No major defects – The formulas assume sound, usable wood.

Data Sources and Authority

These formulas are not arbitrary. They’re based on:

• USDA Forest Service Log Scaling Handbook (updated 2023)
• National Hardwood Lumber Association Standards
• International Log Rule (Forest Products Laboratory, 1917)

Limitations to Keep in Mind

• Actual yield varies by sawmill technology – Modern mills with thin-kerf saws and optimized cutting patterns may exceed these estimates.
• Tree species matters – Hardwoods and softwoods have different characteristics, though the formulas don’t distinguish.
• Log quality is not factored in – A log full of knots will yield less usable lumber than a clear log of the same size.
• These are estimates, not guarantees – Always treat board foot calculations as approximations.

Frequently Asked Questions

Q: Why do the three rules give such different results?
A: Each rule was developed at a different time with different assumptions about sawing efficiency and waste. Doyle is the most conservative (especially for small logs), International is the most accurate, and Scribner is a practical middle ground.

Q: Should I measure diameter inside bark or outside bark?
A: Always measure inside bark (DIB). Bark is not usable lumber, and including it will lead to overestimates. If you can only measure outside bark, you’ll need to estimate bark thickness and subtract it.

Q: Do log lengths have to be standard lengths?
A: While standard lengths (8, 10, 12, 14, 16 feet) are most common in the industry, the formulas work for any length. However, non-standard lengths may complicate pricing and sales.

Q: Why does the Doyle Rule underestimate small logs so much?
A: The Doyle formula subtracts 4 inches from the diameter and then squares the result: (D-4)². For a 12-inch log, that’s (12-4)² = 64. For an 8-inch log, it’s (8-4)² = 16. The squaring effect penalizes small diameters heavily. This made sense in 1825 when sawmill technology was inefficient, but it’s outdated today.

Q: Which rule is the most accurate?
A: The International 1/4” Rule is the most scientifically accurate because it’s based on geometric calculations and realistic waste factors. However, “accurate” also depends on the actual sawmill’s equipment and skill. A highly efficient mill might exceed even the International Rule’s estimate.

Q: Can I use these formulas for standing trees?
A: Yes, but you’ll need to estimate the tree’s merchantable height (the usable trunk length) and the diameter at the top of that section. This requires experience and is often done by professional timber cruisers or foresters.

Q: How do knots and defects affect board feet?
A: The standard formulas don’t account for defects. If a log has significant knots, rot, or splits, you may need to manually reduce the calculated board feet by 10-30% depending on severity. Professional log graders assess this during timber sales.

Q: Why measure the small end instead of the large end?
A: The small-end diameter represents the minimum usable diameter throughout the log. It’s the most conservative and fair measurement. Using the large end would overestimate the lumber yield, especially in tapered logs.

Conclusion: Master Log Scaling for Better Timber Decisions

Understanding how to calculate board feet in logs empowers you to make informed decisions whether you’re buying, selling, or processing timber. Here are the key takeaways:

• Logs require special scaling rules because they’re irregular, tapered, and contain waste.
• Three main rules exist: Doyle (conservative, popular in the East), Scribner (industry standard), and International (most accurate).
• Always measure the small-end diameter inside bark and use standard log lengths when possible.
• Choose your rule based on region, log size, and industry standards in your area.
• These are estimates – actual lumber yield depends on sawmill efficiency and log quality.

Whether you’re a landowner evaluating your timber’s worth, a sawmill operator planning production, or a woodworker sourcing raw logs, mastering log scaling gives you the knowledge to negotiate fairly and plan accurately.

Disclaimer: The formulas and methods provided in this guide are for educational and estimation purposes only. Actual lumber yield is affected by many factors including sawmill equipment, operator skill, log quality, and species characteristics. This article does not constitute professional forestry or timber appraisal advice. For commercial timber sales, consult a certified forester or professional log scaler.

Last Updated: October 2025
Sources: Formulas verified against USDA Forest Service Log Scaling Handbook and National Hardwood Lumber Association standards.