Biochar Blend Calculator Guide
Use this biochar blend calculator to mix biochar, compost, and base soil at custom percentages. Enter total volume in cubic feet and set biochar and compost sliders (combined ≤ 100%) to get component volumes for enriched garden soil.
How to use the biochar blend calculator
Enter total desired blend volume in cubic feet. Adjust biochar and compost percentages — combined they must not exceed 100%. Base soil fills the remainder.
Results show cubic feet of biochar, compost, and topsoil or base soil to measure and mix.
Biochar blend formula
Biochar (cu ft) = Total volume × (Biochar % ÷ 100). Compost (cu ft) = Total volume × (Compost % ÷ 100). Base soil = Total volume − Biochar − Compost.
- Biochar cu ft = total × (biochar% / 100)
- Compost cu ft = total × (compost% / 100)
- Base soil = total − biochar − compost
- Typical biochar: 5–15% of blend by volume
Worked example
Blending 10 cubic feet at 10% biochar and 20% compost: Biochar = 10 × 0.10 = 1 cu ft.
Compost = 10 × 0.20 = 2 cu ft. Base topsoil = 10 − 1 − 2 = 7 cu ft. Mix thoroughly and moisten before use.
Why add biochar
Biochar is porous charcoal that improves water retention, nutrient holding, and habitat for soil biology when charged with compost or nutrients. Fresh biochar can temporarily tie up nitrogen — pre-charge by soaking in compost tea or mixing with compost weeks before planting.
Application tips
Incorporate into the root zone rather than leaving as a topdress layer. One application lasts years — biochar does not decompose quickly. Pair with soil amendment calculator for percentage-based top-dressing math.
- Use horticultural-grade biochar, not BBQ briquettes.
- Charge biochar before applying to avoid nitrogen draw-down.
- Combine with gypsum on heavy clay per soil test.
- 10 cu ft ≈ 0.37 cubic yards for bulk ordering.