Hugelkultur Bed Material Calculator

Hugelkultur (German for “mound culture”) is a raised-bed method that stacks logs and woody debris as a core, then covers it with soil and organic matter. As the wood decomposes it can improve water storage and nutrient cycling, but it also settles over time. Because sourcing logs, branches, and soil often determines what you can build, an up‑front material estimate is useful for planning collection, transport, and site prep.

What this calculator estimates

This page estimates:

• Total mound volume (m³) based on bed length, base width, and height.
• Wood-core volume (m³) using a user-specified wood volume fraction.
• Soil/cover volume (m³) as the remainder of the mound volume.
• Optional mass estimates (kg) using typical bulk density assumptions for mixed wood and moist soil.

Geometric model (triangular prism)

The bed is modeled as a long ridge with a triangular cross-section (a common “pile-and-cover” hugelkultur shape). With:

• L = bed length
• w = base width
• h = bed height

the triangular cross-section area is:

and the total mound volume is:

Wood fraction and split into wood vs. soil

The wood volume fraction (f) is the share of the mound’s geometric volume you want to attribute to logs/branches/woody debris. It’s entered as a decimal between 0 and 1 (for example, 0.40 means 40% wood by volume).

• Wood volume: V_wood = f × V
• Soil/cover volume: V_soil = (1 − f) × V

In real builds, there are also voids (air gaps) between logs, plus finer organic layers. Depending on how you pack the mound, those voids may later fill with soil, compost, or settle. The fraction is a practical “knob” that lets you match your construction style.

Mass estimates (optional)

If mass is shown, it’s computed from a bulk density assumption:

• Mixed wood (logs/branches): ~500 kg/m³ (varies widely by species and moisture)
• Moist soil/topsoil: ~1200 kg/m³ (varies with texture, compaction, and moisture)

Then:

• Mass_wood = V_wood × ρ_wood
• Mass_soil = V_soil × ρ_soil

How to interpret results

• Total volume helps you sanity-check the overall mound size and compare against truckloads, bulk bags, or on-site soil availability.
• Wood volume approximates how much log/branch material you need. If you measure wood in “piles,” estimate the pile’s volume and apply a packing factor (loose stacks can contain significant air space).
• Soil volume approximates how much cover material you need (soil + compost + mulch layers). If you are using multiple layers, treat this as the combined total.
• Mass is most useful for transport planning (vehicle payload limits) and effort planning (moving soil by hand is labor-intensive).

Worked example

Suppose you plan a bed with:

• Length L = 5 m
• Base width w = 1.5 m
• Height h = 1.0 m
• Wood fraction f = 0.40

Total volume:

• V = 0.5 × 1.5 × 1.0 × 5 = 3.75 m³

Split by fraction:

• V_wood = 0.40 × 3.75 = 1.50 m³
• V_soil = 0.60 × 3.75 = 2.25 m³

Mass (using the typical densities above):

• Mass_wood ≈ 1.50 × 500 = 750 kg
• Mass_soil ≈ 2.25 × 1200 = 2700 kg

Quick comparison: changing the wood fraction

The table below keeps L = 5 m, w = 1.5 m, h = 1.0 m (so V = 3.75 m³) and varies only the wood fraction.

Assumptions and limitations (important)

• Triangular cross-section: The model assumes straight sides and a pointed ridge. Rounded/flattened tops or terraced sides will change the true volume.
• Uniform dimensions along the length: Real mounds often taper at the ends; if your bed has rounded ends, your actual volume may be lower than the prism estimate.
• Wood fraction is an approximation: Large logs create voids; small branches pack more tightly. The fraction does not explicitly model air gaps or later infill.
• No compaction modeled: Soil settles after watering and over time. Likewise, the mound height typically shrinks as wood decomposes.
• Fixed densities: Wood and soil density vary by species, moisture content, soil texture, and compaction. Treat mass outputs as planning-level estimates.
• Excludes trenches/berms: If you dig a trench and mound above grade, you may be moving soil rather than importing it; the calculator does not split cut vs. fill.
• Not a structural/engineering tool: For steep, tall mounds on slopes, stability and erosion control may require additional design considerations.

Tips for better estimates

• Measure width at the base where the mound meets existing grade.
• If your top is flat, consider using a smaller “effective height” (or reduce the wood fraction) to approximate the missing triangular tip.
• If you expect significant settling, consider building taller initially and re-checking volume with that “fresh build” height.
• When sourcing soil by the cubic yard, remember: 1 yd³ ≈ 0.7646 m³.