Hoppus CalculatorQuarter-Girth Volume Formula
Official British standard for round timber. Still widely used in India for imported logs and IS 1902 comparisons. Calculates Hoppus feet and Hoppus metre with INR pricing.
Why this calculation matters
Hoppus under-measures round volume by about 21%. Buying on Hoppus and costing on true m³ silently moves your margin.
Hoppus Calculator
Quarter-Girth Volume Formula
This picker does not change the answer. Hoppus feet depends only on the dimensions you enter, not on the species — that is what makes it a rule rather than an estimate. The species is here so you can note it on a printout.
Measure circumference at the exact mid-point of the log.
About Hoppus Calculator
Standardised by Edward Hoppus in 1736. Calculates log volume using girth at the midpoint. Hoppus feet represent approximately 78.54% of true cylindrical volume, accounting for bark and round log wastage. Still official in UK, widely used in India for imported round wood documentation at Kandla, Nhava Sheva and Mumbai. If the hoppus measurement formula has ever puzzled you, the quarter girth calculation is done for you here — enter girth and length, read the volume.
Where Used?
Formulas
Hoppus Feet = (G/4)^2 x L / 144 G = girth inches, L = length feetHoppus Metre = (G/4)^2 x L / 10000 G = girth cm, L = length metresTrue volume = Hoppus x (4/pi) = Hoppus x 1.27321 Hoppus foot = 0.02832 m3 | 1 BF = 2359 cm3- Hoppus system (published formula)
Formula checked against the sources above by an automated regression test (tests/test-calculators.js) that derives each expected value independently of this page. Last reviewed .
FAQ
Wood species data
Density, hardness and movement for 60 timbers
How the calculation works
The girth is divided by four, squared, and multiplied by the length. Squaring a quarter of the girth is the same as pretending the round log is a square beam that would fit inside it — which is roughly what a mill can actually saw out, and why the figure lands about a fifth below true round volume.
Show the formula
Quarter girth = girth / 4 (where a diameter is entered, girth = diameter x pi). Metric: Hoppus m3 = (quarter girth cm)^2 x length m / 10,000. Imperial: Hoppus feet = (quarter girth in)^2 x length ft / 144.The quarter-girth method deducts about 21% against true geometric volume. That deduction is intentional in the Hoppus system and is not an error.
References and what each one provides
- Indian Timber Trade practiceTrade convention, IndiaThe quarter-girth convention and its deliberate ~21% deduction.
Unverified values are marked as such rather than presented as sourced.
Limitations of this calculation
Applies the Hoppus quarter-girth convention, which deliberately deducts about 21% of true round volume. It does not account for sweep, ovality, defect, or actual sawn recovery, which will differ from both figures.
Do not use this for Contract scaling without written agreement on the measurement basis and whether girth is taken over or under bark.
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.
How to use this tool
- Enter the log measurements below, then press Calculate.
- Pick your measurement input from the dropdown.
- Fill in log length, number of logs, price per hoppus foot, price per m3.
- Press Calculate.
Worked example
Common mistakes to avoid
- Treating Hoppus volume as true volume. Hoppus gives about 78.5% of true cylinder volume by design.
- Measuring girth with a slack tape. Pull the tape snug at the mid-point — a loose tape adds phantom volume.
- Confusing Hoppus feet with cubic feet in a contract. Name the unit in writing; the difference is over 20%.