Solutions for Sustainable Living
Soil Volume Calculator
How much soil do you need for your raised garden bed, planter box or pot?
1. Choose a garden bed or planter style
2. Select the shape
3. Enter the measurements
How much do you need?
Your ideal soil mix:
How the calculation works
This document describes the exact math behind the calculator so the logic can be reviewed for correctness. All volumes are computed in cubic feet first, then converted to cubic yards.
1. Units by style
The chosen style determines how the length and width inputs are interpreted. Depth is always entered in inches.
| Style | Length / Width | Depth |
|---|---|---|
| Raised Garden Bed | feet | inches |
| Pot / Elevated Planter | inches | inches |
Every dimension is first converted to feet:
depth_ft = depth_in / 12 length_ft = (style == pot) ? length_in / 12 : length_ft width_ft = (style == pot) ? width_in / 12 : width_ft2. Volume by shape (cubic feet)
For circle, the length input is the diameter. For hexagon, the length input is the side length of a regular hexagon. Width is only used (and only required) for square and rectangle.
square / rectangle: V = length_ft × width_ft × depth_ft circle: V = π × (length_ft / 2)² × depth_ft hexagon: V = (3/2) × √3 × length_ft² × depth_ftThe hexagon area term (3/2)·√3·s² is the standard area of a regular hexagon with side s.
3. Convert to cubic yards
One cubic yard equals 27 cubic feet (3 ft × 3 ft × 3 ft):
cubic_yards = cubic_feet / 27No rounding is applied before this division — values are computed at full precision and only rounded to one decimal place for display. (An earlier version rounded cubic feet up with ceil() before dividing, which badly over-estimated small pots; that step has been removed.)
4. Ideal soil mix split
The total volume is split into a recommended planting mix. The three parts always sum to 100% of the total volume:
| Component | Share | Formula |
|---|---|---|
| Soil | 50% | total × 0.50 |
| Compost | 30% | total × 0.30 |
| Potting mix | 20% | total × 0.20 |
Each component is reported both in cubic yards (large number) and cubic feet (smaller line), derived from the same total.
5. Validation
Length and depth are always required and must be valid numbers. Width is required only for square and rectangle (it is hidden and ignored for circle and hexagon). If a required field is empty or non-numeric, the calculation is blocked and an inline error is shown.
Worked example
Raised bed · rectangle · length 4 ft, width 3 ft, depth 12 in:
depth_ft = 12 / 12 = 1 V = 4 × 3 × 1 = 12 cubic feet cubic_yards = 12 / 27 = 0.44 ≈ 0.4 soil 50% = 6.0 cf | compost 30% = 3.6 cf | potting 20% = 2.4 cfCompetitor research & improvement ideas
Review of the top-10 Google results (US) for the query soil calculator, captured to guide the calculator's roadmap. Each competitor was inspected for the features it offers.
Top-10 results and standout features
| # | Site | Standout features |
|---|---|---|
| 1 | gardeners.com | Raised-bed / pot style toggle (same as ours), 60/30/10 mix, fertilizer amounts, social share |
| 2 | inchcalculator.com | Unit switcher (in/ft/yd/cm/m), direct area input, weight in tons via density, bags needed, embeddable widget, formulas, FAQ |
| 3 | lowes.com | Bulk vs bagged mode, product picker from catalog, add-to-cart |
| 4 | soilcalculator.com | Quantity (N identical containers), bags needed across 4 bag sizes (0.75 / 1 / 1.5 / 2 cu ft) |
| 5 | omnicalculator.com | Metric + imperial, weight via density, cost estimate (price → total), bags, large FAQ |
| 6 | mahoneysgarden.com | By-the-bag / by-the-yard toggle, material selection |
| 7 | soildirect.com | Cubic yards → tons, price & delivery |
| 9 | squarefootgardening.org | Live auto-calculation, mix shown in 5-gallon buckets, charts of common bed sizes |
(#8 is a YouTube video; #10 is the inchcalculator app on Google Play.)
Improvement ideas — high priority
Common to most competitors, currently missing here:
- "How many bags" — a table of bag counts for 0.75 / 1 / 1.5 / 2 cu ft bags. The most common competitor feature, and it drives bag purchases.
- Quantity / multiple beds — a "number of identical beds" field and/or "add another bed" with summed totals.
- Bulk vs bagged — two modes: bulk (cubic yards) and bagged (number of bags), covering both buying scenarios.
Improvement ideas — medium priority
- Unit switcher — at least add cm/m, ideally a dropdown (in/ft/yd/cm/m) like inchcalculator, to serve metric regions.
- Live calculation — recalculate as the user types instead of requiring a Calculate click.
- Cost estimate — optional "price per bag / per cubic yard" field → total cost, prefilled with real product prices.
- Direct area input — enter square feet directly as an alternative to length × width for irregular shapes.
Improvement ideas — SEO / growth
- Public FAQ + content + Schema.org (
HowTo/FAQPage) — top results carry rich copy; the biggest ranking gap for us. - Embeddable widget — "embed this calculator" earns backlinks (inchcalculator's tactic).
- Mix-to-product links — link each 50/30/20 component to a specific product instead of one generic CTA.
Improvement ideas — optional
- Weight in tons/lbs via density — useful when ordering bulk with delivery.
- Depth guidance — placeholder defaults and hint text (competitors suggest "2–4"").
Where we already lead
- Four shapes including hexagon — most competitors offer 1–3 (usually rectangle only).
- Clean branded design and an explicit 50/30/20 mix breakdown.