How to Use the Raised Bed Compost Calculator

This Raised Bed Compost Calculator helps you determine the amount of compost needed for your raised garden bed based on its size, the type of plants you’re growing, and your local climate conditions. Follow these steps to get an accurate estimate:

Step 1: Enter Your Bed Dimensions

• Bed Length (feet): The length of your raised garden bed.
• Bed Width (feet): The width of your raised garden bed.
• Bed Depth (inches): The depth of your raised bed. This helps determine the total soil and compost volume.

Step 2: Select Plant Type

• Leafy Greens: Includes crops like lettuce, spinach, and kale. These generally require more compost to retain moisture and nutrients.
• Root Vegetables: Includes carrots, beets, and radishes. These need less compost since they grow deeper into the soil.
• Fruit-Bearing Vegetables: Includes tomatoes, peppers, and cucumbers. These benefit from a moderate compost depth.

Step 3: Choose Your Climate

• Wet: If you live in a humid or rainy climate, compost depth may not need to be as thick.
• Dry: In dry or arid regions, additional compost can help retain moisture.
• Moderate: For balanced climates with average rainfall and temperatures.

Step 4: Select Soil Status

• Empty Raised Bed: If you’re starting fresh with an empty bed, more compost is required.
• Amending Last Year’s Soil: If you’re refreshing an existing raised bed, less compost is needed since you are only topping up nutrients.

Step 5: Click “Calculate”

Once you’ve filled in the details, press the Calculate button, and the calculator will provide:

• Total Compost Needed (in cubic feet)
• Estimated Compost Bags Needed (based on 1 cubic foot per bag)

Keep In Mind:

This calculator estimates how much compost you need based on your raised bed’s dimensions, plant type, climate, and soil status. Rather than filling your entire bed with compost, it assumes only a portion is compost, and the rest is soil or other organic matter.

That’s because most plants do well in a blend that includes compost but isn’t 100% compost. Soil generally contains sand, silt, clay, and some organic materials. Compost is concentrated organic matter, rich in nutrients that improve soil structure and plant growth. When you add compost, you’re enriching the existing soil or a basic topsoil blend, ensuring plants get the nutrients they need while retaining good drainage and avoiding nutrient overload.

In simpler terms, this calculator looks at your plant type (greens, roots, or fruit-bearing), your climate (wet, dry, or moderate), and whether you’re starting fresh or amending an existing bed. It then figures out a suitable compost layer depth—without exceeding your bed’s total depth—and calculates how many cubic feet (or bags) of compost you’ll need.

It also shows your bed’s total soil volume, so you know how much space you’re filling overall. This way, you give your plants enough nutrients from compost without risking poor drainage or nutrient imbalances from using too much.

Use this information to plan your compost purchase and ensure your plants get the nutrients they need to thrive!