| Total volume | Biochar % | Compost % | Soil % | Biochar density | Compost density | Soil density | Biochar volume | Compost volume | Soil volume |
|---|---|---|---|---|---|---|---|---|---|
| 100 L | 10% | 20% | 70% | 200 kg/m³ | 600 kg/m³ | 1300 kg/m³ | 10 L | 20 L | 70 L |
1) Convert total volume to cubic meters
Total (m³) = Total (selected unit) × unit conversion factor.
2) Compute component volumes by ratio
Biochar (m³) = Total (m³) × Biochar% / 100
Compost (m³) = Total (m³) × Compost% / 100
Soil% = 100 − Biochar% − Compost%
Soil (m³) = Total (m³) × Soil% / 100
3) Convert volume to weight
Weight (kg) = Volume (m³) × Bulk density (kg/m³).
If density is entered in lb/ft³, it is converted to kg/m³ first.
- Enter the total mix volume you plan to blend.
- Select the volume unit you prefer for measuring materials.
- Set biochar and compost percentages by final mix volume.
- Review the computed soil percentage, then adjust if needed.
- Enter bulk densities to estimate weights for buying and hauling.
- Optional: add a charging ratio for liquid used to pre-soak biochar.
- Press Calculate to see results above this form.
- Download CSV or PDF for record keeping and sharing.
Why biochar ratios matter in garden mixes
Biochar changes how a mix holds water, air, and nutrients. Too little may be unnoticeable, while too much can dry seedlings or dilute fertility. A ratio calculator helps you scale the same performance from a test bucket to a full bed by converting percentages into measured volumes and estimated weights. It makes comparisons between amendments consistent when switching from liters to gallons or cubic feet.
Selecting a practical percentage for your crop
Most home gardens perform well with 5–15% biochar by volume when paired with compost. Start lower for fine-seeded crops and higher for woody perennials or sandy soils. If you already use rich compost, reduce biochar slightly to avoid pushing total porosity too high. Keep compost and biochar together below 30% for balanced structure. Record successful mixes, then reuse the same percentages each season as conditions and inputs change.
Using bulk density to plan purchases accurately
Garden materials are usually bought by bag size, but hauling is limited by weight. Bulk density connects volume to kilograms so you can estimate how many bags you need and whether transport is realistic. Wet compost can be much heavier than dry compost, so entering your best density estimate improves budgeting and avoids under-ordering at delivery time.
Charging biochar to protect early plant growth
Fresh biochar can temporarily adsorb soluble nutrients. Charging means pre-soaking biochar with compost tea, diluted fertilizer, or nutrient-rich water so the carbon surfaces are already occupied. The calculator’s charging estimate gives a working liquid target based on biochar volume. Drain well before mixing so the final blend stays workable and aerated.
Interpreting results for beds, pots, and compost
Use the output volumes to measure materials with buckets, tubs, or wheelbarrows in the chosen unit. Compare the weight totals to your lifting limits and container ratings. If the soil portion looks low, reduce compost or biochar rather than eliminating soil. For compost piles, use lower biochar rates to preserve heat and moisture.
1) What biochar percentage is a safe starting point?
Start with 5–10% by volume for most gardens. If plants respond well and moisture stays stable, you can move toward 15%. Use smaller trials for seedlings and salty or alkaline soils.
2) Should I replace compost with biochar?
No. Compost supplies nutrients and biology, while biochar mainly improves structure and nutrient retention. Use both, and keep enough compost for fertility. Adjust percentages so the soil portion remains substantial.
3) Why does the calculator ask for bulk density?
Density converts volume into weight, which helps estimate bag counts, delivery loads, and lifting limits. It is especially useful when compost moisture varies or when you are blending large batches.
4) What does “charging” biochar mean?
Charging pre-loads biochar with nutrients by soaking it in compost tea or diluted fertilizer. This reduces early nutrient adsorption and supports quicker plant establishment, especially in low-fertility mixes.
5) Can I use this for potting mixes?
Yes. Use conservative rates, usually 5–12% biochar, and maintain enough compost or slow-release nutrition. Potting mixes dry faster, so monitor watering and avoid overly high porosity.
6) Do I need exact densities to get useful results?
Exact values are not required. Use reasonable estimates or supplier specs, then refine after weighing a known volume. The ratio volumes will still be correct; density mainly affects weight planning.