Calculate Soil for Raised Bed

by

Raised Garden Bed Soil Calculator

Soil Requirements:

function calculateSoil() { var bedLength = parseFloat(document.getElementById('bedLength').value); var bedWidth = parseFloat(document.getElementById('bedWidth').value); var bedDepth = parseFloat(document.getElementById('bedDepth').value); var soilResultDiv = document.getElementById('soilResult'); var resultCubicFeet = document.getElementById('resultCubicFeet'); var resultCubicYards = document.getElementById('resultCubicYards'); var resultBags1_5 = document.getElementById('resultBags1_5'); var resultBags2_0 = document.getElementById('resultBags2_0'); if (isNaN(bedLength) || isNaN(bedWidth) || isNaN(bedDepth) || bedLength <= 0 || bedWidth <= 0 || bedDepth <= 0) { soilResultDiv.style.display = 'block'; resultCubicFeet.innerHTML = 'Please enter valid positive numbers for all dimensions.'; resultCubicYards.innerHTML = "; resultBags1_5.innerHTML = "; resultBags2_0.innerHTML = "; return; } // Convert depth from inches to feet for consistent units var bedDepthFeet = bedDepth / 12; // Calculate total volume in cubic feet var volumeCubicFeet = bedLength * bedWidth * bedDepthFeet; // Convert to cubic yards var volumeCubicYards = volumeCubicFeet / 27; // Calculate number of bags (rounding up as you can't buy partial bags) var bags1_5cuft = Math.ceil(volumeCubicFeet / 1.5); // Common bag size var bags2_0cuft = Math.ceil(volumeCubicFeet / 2.0); // Another common bag size soilResultDiv.style.display = 'block'; resultCubicFeet.innerHTML = 'Total Soil Needed: ' + volumeCubicFeet.toFixed(2) + ' cubic feet'; resultCubicYards.innerHTML = 'Equivalent: ' + volumeCubicYards.toFixed(2) + ' cubic yards'; resultBags1_5.innerHTML = 'Approx. 1.5 cu ft bags: ' + bags1_5cuft + ' bags'; resultBags2_0.innerHTML = 'Approx. 2.0 cu ft bags: ' + bags2_0cuft + ' bags'; }

Calculating Soil for Your Raised Garden Bed

One of the most common questions for new and experienced gardeners alike is, "How much soil do I need for my raised bed?" Getting this right is crucial for both your budget and the health of your plants. Over-ordering means wasted money and excess soil, while under-ordering means multiple trips to the garden center and delays in planting.

Why Accurate Soil Calculation Matters

Raised garden beds offer numerous benefits, including better drainage, warmer soil temperatures, and easier access for planting and harvesting. However, they require a significant amount of soil to fill. Unlike in-ground gardens, you're essentially creating a contained growing environment from scratch. Knowing the exact volume ensures you purchase the right amount of soil, compost, and amendments, saving you time, effort, and money.

How to Measure Your Raised Bed

To use the calculator above, you'll need three basic measurements:

  1. Length: Measure the longest side of your raised bed in feet.
  2. Width: Measure the shorter side of your raised bed in feet.
  3. Depth (or Height): Measure the vertical height of your raised bed walls in inches. This is how deep the soil will be.

Ensure your measurements are accurate. Even a small error can lead to a noticeable difference in the total soil volume required.

The Basic Formula

The calculator uses a simple volume formula: Volume = Length × Width × Depth. Since garden bed dimensions are often given in feet for length and width, and inches for depth, the calculator converts the depth to feet before performing the multiplication to ensure consistent units (cubic feet).

Once the volume in cubic feet is determined, it's converted into more practical units like cubic yards (for bulk purchases) and the number of common soil bag sizes (1.5 cu ft and 2.0 cu ft), always rounding up to ensure you have enough.

Example Calculation

Let's say you have a raised bed with the following dimensions:

  • Length: 4 feet
  • Width: 8 feet
  • Depth: 12 inches

Using the calculator:

  1. Depth in feet: 12 inches / 12 = 1 foot
  2. Volume in cubic feet: 4 feet × 8 feet × 1 foot = 32 cubic feet
  3. Volume in cubic yards: 32 cubic feet / 27 = 1.19 cubic yards
  4. Number of 1.5 cu ft bags: 32 / 1.5 = 21.33, rounded up to 22 bags
  5. Number of 2.0 cu ft bags: 32 / 2.0 = 16 bags

So, for this bed, you would need approximately 32 cubic feet of soil, which is about 1.19 cubic yards, or 22 bags if buying 1.5 cu ft bags, or 16 bags if buying 2.0 cu ft bags.

Tips for Filling Your Raised Bed

  • "Lasagna Gardening" Method: To reduce the amount of expensive bagged soil needed, consider filling the bottom third to half of your raised bed with organic materials like logs, branches, leaves, straw, and unfinished compost. This method, often called "lasagna gardening," provides excellent drainage, slowly releases nutrients, and reduces your soil costs.
  • Soil Mix: Don't just use topsoil. A good raised bed mix typically consists of a blend of high-quality topsoil, compost, and possibly some perlite or vermiculite for aeration and moisture retention. Aim for about 30-50% compost in your initial fill.
  • Settling: Soil will settle over time, especially after watering. It's wise to fill your bed slightly above the desired final level, knowing it will compact. You may need to top it off with more compost or soil in subsequent seasons.
  • Source Your Soil: For large beds, buying soil in bulk by the cubic yard from a local landscape supply company can be significantly more cost-effective than buying individual bags.

By using this calculator and following these tips, you'll be well on your way to a thriving raised garden bed!

Leave a Comment