Raised Bed Soil Calculator
Use this raised bed soil calculator to find out exactly how much soil you need — with an optional Mel's Mix breakdown for the perfect growing medium.
1Raised Bed Dimensions
Common depths: 6 in for herbs, 12 in for vegetables, 18-24 in for deep-rooted crops
2Soil Mix Settings
For a custom blend, enter what percentage of total volume each component is. Must add up to 100%.
Your Soil Estimate
Mel's Mix Breakdown
Your Custom Mix Breakdown
Tip: Soil settles 10–15% after the first watering and frost cycle. Consider topping up in spring with a 1–2 inch layer of compost each year to maintain soil level and fertility.
How to Use This Calculator
Using this raised bed soil calculator ensures you buy the exact amount of dirt and soil amendments for your garden. Follow these five steps:
- 1Measure bed length and width. Take the inside measurements of your garden bed in feet and inches.
- 2Measure wall height. Enter the height of the bed walls, which equates to the total depth of soil needed to fill the box to the brim.
- 3Multiply identical beds. If you are building several beds of the exact same size, simply increase this number to calculate your total volume at once.
- 4Choose your mix type. Select standard bagged soil or a custom blend. Mel's Mix is a famous, highly popular raised bed recipe (one-third blended compost, one-third peat moss, one-third vermiculite) that retains moisture perfectly, stays incredibly loose, and never compacts.
- 5Select bag size or bulk. Choose the bag size available at your local nursery, or select the bulk option if you are ordering soil by the cubic yard for delivery.
The Formula
This raised bed soil calculator uses straightforward geometric formulas to find your required material volume:
Volume (Cubic Feet) = Length × Width × Depth (all measured in feet)
Cubic Yards = Cubic Feet / 27
Bags = Cubic Feet / Bag Size (rounded up)
First, the volume in cubic feet equals your bed's length times its width times its depth. To find your cubic yards for bulk ordering, that cubic foot total is divided by 27. For bags, the total cubic feet is divided by the size of the bag you selected, rounded up to the nearest whole bag. If you choose the Mel's Mix breakdown, the total cubic feet is simply divided by 3 to provide equal parts of compost, peat moss, and vermiculite. Keep in mind that freshly mixed raised bed soil contains a lot of air and will naturally settle by 10% to 15% after the first season, so topping up annually with compost is recommended.
Frequently Asked Questions
How deep should a raised bed be?
A depth of 6 to 8 inches is sufficient for shallow-rooted herbs, lettuces, and spinach. For standard vegetables like tomatoes, peppers, and cucumbers, a 12-inch depth is ideal. For deep-root vegetables like carrots, parsnips, or potatoes, you should build your beds 18 to 24 inches deep.
Should I put cardboard or landscape fabric at the bottom?
Always use uncoated, plain brown cardboard at the bottom of a new raised bed. Cardboard effectively smothers existing grass and weeds but breaks down over a few months, allowing deep roots and beneficial earthworms to pass through. Landscape fabric creates a permanent, unnatural barrier that disrupts soil biology and limits root expansion.
What is Mel's Mix, and is it worth the cost?
Mel's Mix is a premium soil recipe from the creator of Square Foot Gardening: 1/3 blended compost, 1/3 coarse vermiculite, and 1/3 peat moss. While buying these individual components is more expensive upfront than cheap bagged soil, it is highly worth it. The mix drains perfectly, holds moisture like a sponge, and stays light and fluffy for years without ever needing to be tilled.
Can I use topsoil from my yard in a raised bed?
You should avoid using straight native topsoil in a raised box. Yard dirt is dense, heavy, and lacks the proper drainage for a confined space. It will quickly compact into concrete-like blocks, suffocating plant roots. If you must use native soil to save money, amend it heavily with at least 30% compost and aeration materials like perlite.
How often should I replenish or top up the soil?
Raised bed soil settles and organic matter breaks down continuously, meaning you should plan to top up your beds every single spring. Simply add a 1 to 2-inch layer of fresh, high-quality compost to the surface. This restores the soil level and provides fresh nutrients for the new season.
Does raised bed soil need fertilizer?
Yes. Because raised beds drain water so efficiently, water-soluble nutrients wash out of the bottom of the bed much faster than they would in an in-ground garden. You should amend your soil with a balanced organic slow-release fertilizer at planting time, and feed heavy-producing crops like tomatoes mid-season.