Plan castings before planting, mixing, or topdressing. Choose crops, container size, and application frequency easily. Avoid waste, improve soil life, and feed roots evenly.
| Scenario | Inputs | Typical output |
|---|---|---|
| Topdress bed | 100 sq ft, 0.25 in layer | ~59 L (about 15.6 gal) |
| Mix into soil | 50 sq ft, 6 in depth, 10% | ~85 L (about 22.4 gal) |
| Containers | 6 pots, 3 gal each, 15% | ~10.2 L (about 2.7 gal) |
| Batch potting mix | 20 gal batch, 15% | ~11.3 L (about 3.0 gal) |
| Tea style | 5 gal water, 1 cup/gal | ~1.18 L (about 5 cups) |
Topdress (layer method): Volume = Area × Thickness.
Mix-in (percent of soil volume): Soil Volume = Area × Depth, Castings Volume = Soil Volume × (Percent ÷ 100).
Containers: Castings Volume = (Pots × Pot Volume) × (Percent ÷ 100).
Batch mix: Castings Volume = Batch Volume × (Percent ÷ 100).
Weight estimate: Weight = Castings Volume (L) × Density (kg/L). A settling buffer multiplies final volume.
Worm castings work best when you match the application method to plant demand. Topdressing delivers microbes and gentle nutrients at the soil surface, where irrigation carries them downward. Mixing into the root zone supports new beds and renovations, but excessive percentages can reduce drainage in heavy media. This calculator separates these methods so you can plan realistic volumes before you open a bag. It helps schedule deliveries and storage space for castings.
Volume planning is more reliable than guessing by “handfuls.” Beds and lawns are calculated from area and layer thickness, producing liters and gallons you can measure with buckets. Soil mix-in uses amended depth to estimate soil volume, then applies a chosen percentage. Container and batch modes scale the same logic to repeated pots or a single blending session, reducing last-minute shortages. Shows quarts for smaller batch measuring.
Density varies by moisture, screening, and storage. The weight estimate converts volume to kilograms and pounds using a selectable bulk density, making it easier to order by weight-based products. If your castings feel damp and compact, increase density; if they are dry and fluffy, reduce it. The settling factor adds a practical buffer for compaction during transport and spreading. Test-scoop to calibrate density for material.
For established vegetables, a thin topdress often supports steady growth without pushing soft foliage. For seedlings and small pots, lower rates prevent overly rich mixes. For fruiting crops, small repeat applications can be safer than one heavy dose. The calculator’s percent ranges help you stay within conservative limits while still improving aggregation, water retention, and nutrient cycling in most soils. Sandy beds may need thicker layers.
Consistent measurement supports repeatable gardening outcomes. Save your inputs and outputs as CSV for seasonal records, then compare results across beds, crops, and years. Use the PDF plan when purchasing, staging bins, or allocating castings among zones. When you change only one variable—thickness, percent, or pot count—you can see the impact instantly and choose the most efficient approach.
For most beds, start with 0.125 to 0.25 inch as a light layer. Use thinner amounts around seedlings. Reapply later if plants respond well and soil stays well-aerated.
Many gardeners stay near 5–15% by volume for routine improvement. Use lower percentages in heavy clay or fine potting mixes. Increase gradually only after observing drainage and plant vigor.
Castings can be fluffy or compact depending on moisture and screening. Density converts volume into weight so you can purchase accurately when products are sold by kilograms or pounds.
If you pack castings tightly, transport long distances, or measure with small containers, a buffer helps. Keep it near 1.00 for careful measuring, or raise it to 1.10–1.20 for loose handling.
Enter the number of pots and the volume of each pot, then choose a blend percentage. The calculator multiplies total potting volume by that percentage to return the castings amount.
Yes. Select the tea option and enter water volume and a cups-per-volume rate. The output is an approximate casting volume for measuring, not a guarantee of brew strength.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.