CBM Calculation for Round Logs: Doyle, Scribner, JAS, and Huber Methods Explained

Accurate volume measurement is the foundation of any timber trade. Whether you’re buying logs at the sawmill, loading containers for export, or preparing shipping documentation, you need a reliable, consistent method for calculating the cubic metre volume (CBM) of round logs.

The challenge: there are multiple methods in use globally, and they often produce different results for the same physical log. Understanding the differences — and knowing which method your buyers, freight forwarders, and customs authorities expect — is essential.

Why CBM Matters in Timber Export

CBM determines the value and volume of your shipment. Discrepancies between the seller’s CBM and the buyer’s CBM can lead to disputes, renegotiation, and delays. Getting it right at the tally stage prevents problems downstream.

In timber export, CBM is typically:

• Agreed at contract time — which formula to use is specified in the purchase agreement
• Calculated at loading — the tally team measures each log and records diameter and length
• Verified at destination — the buyer’s team re-measures a sample or the full consignment

Any systematic difference between your method and the buyer’s method translates directly into financial discrepancy.

The Four Main Methods

1. Huber Formula (Most Common in Export Trade)

The Huber formula uses the mid-point diameter of the log:

V = (π / 4) × D² × L

Where:

• V = volume in cubic metres
• D = diameter at the middle of the log, in metres
• L = length of the log, in metres

Example: A log with mid-diameter 48 cm and length 4.2 m:

• D = 0.48 m
• V = (π/4) × 0.48² × 4.2 = 0.762 m³

When to use Huber: European buyers and many Asian buyers use Huber. It’s also the basis for JAS measurement (with modifications). Huber tends to give higher volumes than Doyle and lower than Scribner for the same logs.

2. JAS (Japanese Agricultural Standard)

JAS is Huber with a specific measurement protocol:

• Diameter measured to the nearest even centimetre (always round down)
• Length measured to the nearest 0.1 m (round down)
• Bark excluded from diameter measurement

This rounding protocol means JAS volume is systematically slightly lower than pure Huber. Japanese buyers will expect JAS measurement, and most tally sheets going to Japan, Korea, or Taiwan use this standard.

Example (JAS): Actual diameter 49.5 cm, actual length 4.23 m:

• JAS diameter = 48 cm (round down to nearest even)
• JAS length = 4.2 m (round down to nearest 0.1)
• V = (π/4) × 0.48² × 4.2 = 0.762 m³

If you had used 49 cm: V = (π/4) × 0.49² × 4.2 = 0.793 m³ — a meaningful difference at scale.

3. Doyle Formula (North American Origin)

The Doyle formula applies a diameter deduction intended to account for slab and waste:

V = ((D - 4) / 4)² × L / 16

Where D is in inches and L is in feet, giving volume in board feet (BF). To convert to m³: 1 board foot ≈ 0.00236 m³.

When to use Doyle: Primarily used in North America. Doyle significantly underestimates volume compared to Huber or Scribner for small-diameter logs, and overestimates for very large ones. Most international export contracts do not use Doyle, but some North American buyers insist on it.

4. Scribner Decimal C

Scribner is also a North American board foot measure, using tables developed by Scribner in the 1840s. It’s more accurate than Doyle for small logs but still produces different results than metric methods.

When to use Scribner: Primarily for softwood logs sold in North American markets. Not common in South Asian or Southeast Asian timber export.

Practical Considerations for Export Tally

Which Formula Does Your Contract Specify?

Always check the purchase contract. Common scenarios:

• India to Japan/Korea/Taiwan: JAS measurement required
• India to Europe: Huber (metric), with or without specific bark measurement protocol
• India to Middle East: Usually Huber, but verify with buyer
• Domestic Indian trade: Often Huber or JAS depending on buyer preference

Bark vs. Over-Bark Measurement

Most export contracts specify under-bark (UB) diameter measurement. However:

• At loading, it may be impractical to debark every log
• Over-bark (OB) to under-bark (UB) conversions use species-specific bark thickness factors
• Your contract should specify OB or UB — document which you used in the tally sheet

Measurement at Loading vs. Destination

Logs lose moisture weight during transit. Volume doesn’t change, but diameter can shrink slightly as moisture leaves the wood. This is rarely significant for CBM calculations, but it’s worth knowing if a buyer disputes the volume.

How Tally Sheet Software Handles CBM

A good timber management system should:

1. Store the measurement protocol — which formula, OB or UB, rounding method
2. Calculate automatically — no manual formula entry, reducing errors
3. Show running totals — CBM per species, per loading site, per batch
4. Export correctly — PDF and Excel with clearly stated formula and protocol

LumberLinq calculates CBM using the Huber/JAS formula with configurable rounding, displays running totals per species and per loader, and exports tally sheets in buyer-ready PDF format with measurement protocol stated on the document.

Quick Reference: Which Method for Which Market?

Want your tally team to calculate CBM automatically — no formulas, no manual checking? Try LumberLinq free for 14 days.