Calculator
Example data table
| Bed size (L×W×D) | Total volume (ft³) | Compost (ft³) | Peat/Coir (ft³) | Vermiculite (ft³) | Notes |
|---|---|---|---|---|---|
| 4 ft × 8 ft × 0.5 ft | 16.00 | 5.33 | 5.33 | 5.33 | Classic 1:1:1, no waste |
| 3 ft × 6 ft × 0.5 ft | 9.00 | 3.15 | 3.15 | 2.70 | Less verm (1:1:0.75) |
| 2 ft × 4 ft × 0.5 ft | 4.00 | 2.00 | 1.00 | 1.00 | More compost (2:1:1) |
Formula used
- Base volume comes from a direct input, or Length × Width × Depth.
- Adjusted total = Base × (1 + Waste%) × (1 + Compaction%).
- Ingredient volume = Adjusted total × (Ingredient ratio ÷ Sum of ratios).
- Bag count = ceiling(Ingredient liters ÷ Bag liters).
How to use this calculator
- Choose Total volume or Bed dimensions.
- Select a ratio preset, or pick Custom to edit ratios.
- Pick peat moss or coco coir as the base material.
- Set waste and compaction if you want extra buffer.
- Optionally enter bag sizes and prices to estimate totals.
- Press Calculate. Results appear above the form.
Volume planning improves fill accuracy
Raised beds rarely match a single bag size, so planning by volume reduces last‑minute shortages. This calculator accepts cubic feet, cubic yards, liters, gallons, or meters. A 4×8×0.5 ft bed equals 16.00 ft³, then waste and compaction adjust the target. Using 5% waste increases the target to 16.80 ft³, which helps cover settling after watering.
Ratio presets reflect common mixing goals
The classic blend uses equal parts compost, base material, and vermiculite by volume. For faster nutrient buildup, the “more compost” preset shifts to 2:1:1, increasing compost share from 33.3% to 50%. The “less vermiculite” preset uses 1:1:0.75, reducing vermiculite share to 27.3%, which can be useful when vermiculite supply is limited.
Waste and compaction are measurable levers
Waste accounts for spillage, trimming, and uneven blending. Compaction accounts for how firmly you pack materials while filling. If you apply 8% waste and 5% compaction, the multiplier becomes 1.134. That means a 100 L project should be planned as 113.4 L. These two fields make the estimate more realistic across different handling methods.
Bag and cost estimates support purchasing decisions
Bag sizes are entered in liters, then the tool rounds up to whole bags using ceiling math. If compost is 200 L and you buy 40 L bags, the estimate becomes 5 bags. Enter per‑bag prices to calculate line totals and a grand total. This prevents underbuying and allows quick comparisons between peat and coir sources.
Exports create a repeatable mixing record
CSV output works well for spreadsheets and inventory logs, while the PDF summary is convenient for printing at the store. Each export includes adjusted totals, ingredient amounts, ratios, and loss factors. Keeping these records helps you repeat a proven blend for future beds, containers, or seasonal top‑ups with consistent results. If you manage multiple beds, save one PDF per bed to simplify reorders and budgeting next season.
FAQs
What is the standard Mel’s Mix ratio?
The classic approach is equal parts compost, base material, and vermiculite by volume. This tool expresses that as a 1:1:1 preset and converts the result into liters and your selected output unit.
Should I choose peat moss or coco coir?
Either works as the base material by volume. Coir is renewable and rehydrates well; peat is widely available and consistent. Use the same ratio and focus on moisture management and sourcing quality.
How much waste factor should I use?
For careful mixing, 3–5% is common. For large projects, uneven blending, or transport losses, 5–10% is safer. The calculator applies waste before splitting ingredients by ratio.
Why add a compaction factor?
Compaction reflects how tightly materials are packed in the bed. If you press layers firmly, volume shrinks and you need more material. Try 0–5% for light filling, or 5–10% for heavy packing.
How are bag counts calculated?
The tool converts each ingredient to liters, divides by your bag size in liters, then rounds up using ceiling math. That means it always suggests enough bags, even when the last bag is partially used.
Can I export results for purchasing?
Yes. After calculating, download CSV for spreadsheets or PDF for printing. Exports include adjusted totals, ingredient amounts, ratios, waste, and compaction settings for quick store comparisons.