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Mel's Mix Calculator for Raised Beds

Mel's Mix — the soil blend popularized by Mel Bartholomew in his book 'Square Foot Gardening' — consists of equal parts compost, peat moss (or coco coir), and coarse vermiculite. U…

All Shapes Supported Inches, Feet, CM & Meters Bag Count & Cost Estimate

Calculate Your Soil

Enter your raised bed dimensions below

Bed Shape
Measurement Units
Bag Size & Cost Options Optional

Mel's Mix Calculator for Raised Beds

Mel's Mix — the soil blend popularized by Mel Bartholomew in his book 'Square Foot Gardening' — consists of equal parts compost, peat moss (or coco coir), and coarse vermiculite. Use the calculator above to find your total bed volume in cubic feet, then divide by 3 to get the quantity of each component. For a 4×8 bed at 12 inches (32 cu ft): you need about 10.7 cu ft of each ingredient.

How to Use This Calculator

Select your bed shape (Rectangle, Square, or Circle), choose your unit of measurement, then enter your dimensions. For rectangular and square beds, enter length, width, and depth. For circular beds, enter the diameter and depth. Click Calculate Soil Needed to see your results instantly in cubic feet, cubic yards, liters, and gallons — plus bag counts for all four standard bag sizes.

Understanding Your Results

Cubic feet is the unit printed on most bagged soil at garden centers. Use this number to count bags. Cubic yards is the unit used by landscape bulk suppliers — divide cubic feet by 27 to get cubic yards. Liters is the metric equivalent (1 cu ft = 28.32 liters). Gallons is helpful for smaller container calculations (1 cu ft = 7.48 gallons).

Volume Formula (Rectangle)
Volume = Length × Width × Depth (all in feet)

Soil Mix Recommendation

The best all-purpose raised bed mix is 60% quality topsoil, 30% compost, and 10% perlite or coarse sand. This blend drains well, retains moisture, and provides the nutrients plants need. Avoid filling raised beds with pure topsoil — it compacts and restricts root growth. Always include at least 25–30% organic matter.

💡 Order 10% extra: Soil settles 10–15% after the first thorough watering. Buying a little extra prevents a second trip to the store.
Common Questions

Frequently Asked Questions

The best all-purpose raised bed mix is: 60% topsoil, 30% compost, 10% perlite or coarse sand. For a premium option, try Mel's Mix: equal thirds of compost, peat moss (or coco coir), and coarse vermiculite. Avoid filling beds with pure topsoil — it compacts and drains poorly in a raised environment.
Native garden soil on its own is not recommended for raised beds — it tends to compact heavily, restricts root growth, and drains poorly. If you want to incorporate native soil, use no more than 40% mixed with compost and a drainage amendment like perlite or coarse sand.
Most culinary herbs — basil, parsley, cilantro, chives, and dill — thrive in 6–8 inches of well-draining soil. Woody herbs like rosemary, thyme, and sage prefer 10–12 inches. Herbs in general do better in a slightly leaner, well-draining mix than in a rich, moisture-retentive soil.
Soil settles 10–20% after the first thorough watering as air pockets collapse and organic matter starts to break down. This is normal. Always fill your bed to the very top, and plan to top it up with fresh compost after the first watering. The calculator results already assume you fill to the rim, so buy a little extra to account for this settling.
Potting mix is engineered for containers: very light, fast-draining, and often lacking in nutrients for large volumes. Raised bed mix is specifically formulated for elevated garden beds — it balances drainage, water retention, and nutrition at the larger volumes raised beds require. Potting mix in a raised bed would dry out too quickly and cost significantly more per cubic foot.
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