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Vriksai Timber Intelligence

Bark Deduction ToolOver Bark to Under Bark Converter

Calculate bark thickness and bark volume, then convert over-bark measurements to under-bark for accurate timber pricing. Species-specific bark factors for Indian, European and tropical species.

Why this calculation matters

Volume rules want under-bark diameter. Paying for over-bark volume on a thick-barked species is a recurring, invisible loss.

OB to UB ConversionBark Volume %IS 1902 DeductionSpecies Bark FactorsPDF Report
BK

Bark Deduction Tool

Over Bark to Under Bark Converter

Configuration
%

Auto-set by species. You can override manually.

Log Measurements - Over Bark
cm
cm
cm
metres
cm

Enter measured value to override species factor. Leave 0 to use factor.

logs
OK
Bark Deduction Results
-
cm
Bark Thickness Each Side
-
%
Bark Volume %
-
m3
Volume OB
-
m3
Volume UB
PositionOB DiameterBark Each SideUB DiameterArea OBArea UB
Calculation Steps
About Bark Deduction Tool
All log volume formulas can be calculated Over Bark (OB) or Under Bark (UB). For timber pricing, Under Bark volume is the correct basis since bark has no commercial lumber value. This tool converts OB measurements to UB using species-specific bark factors per IS 1902:2015. Scalers call this the DIB from DOB conversion — the bark thickness deduction that turns an over-bark tape reading into true wood diameter.
Where Used?
IS 1902 IndiaLog Purchase PricingImport CustomsTimber AuctionsForest Dept India
Formulas
Bark thickness each side = OB_diameter x bark_factor / 200UB diameter = OB diameter - 2 x bark_thicknessVolume OB = pi x (D_OB_mid / 200)^2 x L (Huber method)Volume UB = pi x (D_UB_mid / 200)^2 x LBark volume % = (V_OB - V_UB) / V_OB x 100
Sources & verification
  • Bark thickness = OB diameter × factor / 200
  • Huber volume on the mid diameter; bark % = 1 − (D_ub/D_ob)²
Formula checked against the sources above by an automated regression test (tests/verify-phase3a.js) that derives each expected value independently of this page. Last reviewed .
FAQ
How does bark affect timber pricing in India?
IS 1902 specifies pricing on Under Bark volume. Buyers paying on OB measurements overpay by 8-16% (the bark volume %). Imported logs from Myanmar, Africa and Malaysia often have thick bark - always convert to UB for internal pricing.
How much does bark thickness vary between species?
Quite a lot, which is why a flat percentage can mislead you. Thin-barked species like young eucalyptus or birch might lose only a few percent of diameter to bark, while thick, corky barks on older pine, oak or many tropical hardwoods can take a much bigger bite. Bark is also thicker at the butt than up the stem. If you're buying regularly from the same source, it pays to measure the actual double-bark thickness on a few representative logs and use that rather than a generic figure.
Is bark always deducted when buying logs?
It depends on how the deal is written. Many contracts price on 'under-bark' (timber only) volume because bark isn't usable lumber, so the bark is deducted. Others price 'over-bark' at a lower rate per unit that already accounts for the waste. Neither is wrong — what matters is that buyer and seller agree which basis they're using before money changes hands, because mixing the two is a common source of invoice disputes.
ResourcesView the formulasFormula Library
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Wood species data
Density, hardness and movement for 60 timbers
Browse all species 
How the calculation works
Bark is subtracted twice from the diameter, once for each side of the log. Because area depends on the square of diameter, a small bark figure removes a disproportionately large share of volume — which is why the percentage lost is always higher than the bark thickness alone suggests.
Show the formula
Diameter inside bark = diameter over bark - 2 x bark thickness, applied at each measurement point. Cross-sectional area = pi x (d/2)^2. Volume = mid-point area x length (Huber). Bark share of volume = (volume over bark - volume inside bark) / volume over bark x 100.
Uses Huber (mid-point) volume. The bark thickness you enter governs the result; published averages vary widely within a species.
References and what each one provides
  • USDA Wood Handbook (FPL GTR-190)USDA Forest Products LaboratoryPublished density, moisture relationships, shrinkage coefficients and mechanical properties for a wide range of species. The reference dataset behind most wood-property figures on this site.
Unverified values are marked as such rather than presented as sourced.
Limitations of this calculation
Applies the bark allowance entered. It does not account for variation around the circumference, between logs in a consignment, or with age, site and species.
Do not use this for Contract deduction without an agreed allowance between buyer and seller.
Figures are engineering estimates from the inputs and assumptions shown. Verify against the actual material and, where the result affects structure or safety, against a qualified professional.
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How to use this tool
  1. Enter the log measurements below, then press Calculate.
  2. Fill in bark factor, ob diameter - small end, ob diameter - mid point, ob diameter - large end. 
  3. Press Calculate. 
Worked example
With the tool's starting values — bark factor = 8, ob diameter - small end = 40, ob diameter - mid point = 48, ob diameter - large end = 58, log length = 5 — pressing Calculate gives: 1.920 cm (bark thickness each side); 15.4 % (bark volume %); 0.90478 m3 (volume ob). 
Common mistakes to avoid