Soil Volume Calculator

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. The shape formulas (rectangle, hexagon, octagon, L and U) follow the approach published in the Eartheasy guide How to Calculate Soil Volume for Raised Garden Beds, and the worked examples in that guide reproduce 1:1 in this calculator.

1. Units by style

The chosen style determines how the length and width inputs are interpreted. Depth is always entered in inches.

Every dimension is first converted to feet:

2. Volume by shape (cubic feet)

For hexagon and octagon, the length input is the side length of the regular polygon. For L-shape and U-shape, the bed is treated as a sum of rectangles — two for L, three for U — and each rectangle is entered separately. Width is required for square, rectangle, L-shape and U-shape (Section 1 width in L/U).

The hexagon area term (3/2)·√3·s² and the octagon area term 2·(1+√2)·s² are the standard areas of regular polygons with side s. The L / U formulas match the standard approach used in published gardening guides — measure each rectangular section, add the areas, multiply by depth. All sections share the same depth.

3. Convert to cubic yards

One cubic yard equals 27 cubic feet (3 ft × 3 ft × 3 ft):

No 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:

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 for square, rectangle, L-shape and U-shape (it is hidden and ignored for hexagon and octagon). For L-shape, Section 2 length and width are also required. For U-shape, Section 2 and Section 3 dimensions are required as well. If any 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:

Competitor 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

(#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

• Six shapes — square, rectangle, hexagon, octagon, L-shape and U-shape — most competitors offer only rectangle.
• Clean branded design and an explicit 50/30/20 mix breakdown.

New calculator opportunities (traffic-validated)

Candidate calculators to build next, validated with Ahrefs. Figures are the estimated US monthly organic traffic of the top-ranking pages for each keyword (i.e. the current SERP leaders, not weak sites). Decision rule: build it if the leading pages clearly exceed 100 clicks/month.

Traffic is each ranking page's total organic traffic (Ahrefs SERP overview, US, monthly). For dedicated single-purpose calculator pages this closely tracks the calculator keyword itself.

Recommended build order

Ranked by traffic × Eartheasy brand fit × reuse of this calculator's code:

1. Mulch — huge traffic, same formula as soil (area × depth → cubic yards / bags), sells mulch. Cheapest to build from this codebase.
2. Compost — strong traffic, core to the sustainable-living brand, same volume formula.
3. Plant spacing — high traffic and strong garden fit; different math (spacing grid / plant count).
4. Grass seed — good traffic; coverage-rate math (seed lbs per area).
5. Gravel / sand / stone — the largest traffic of all, but lower brand fit (landscaping rather than organic gardening). Build if expanding into hardscaping.
6. Fertilizer — decent traffic, but N-P-K dosing is complex and university agronomy tools dominate the SERP (hard to outrank).

Strategy

Shipping 2–3 same-formula calculators (soil → mulch → compost) cross-linked in one shared design forms an SEO cluster that outperforms any single standalone calculator and lifts the whole set.