Raised Bed Soil & Mix Calculator

This raised bed soil calculator estimates the total volume you need and splits it into a custom soil mix for vegetables, herbs, and flowers. Enter each bed’s length, width, and height in meters or feet, include how many copies of that bed you are building, and set a settling percentage to top off after the soil compacts. Then choose your recipe using common ingredients such as screened topsoil, compost, coco coir, perlite, or vermiculite. The tool returns total cubic meters or cubic feet, liters or cubic feet per ingredient, the number of bags to buy based on your bag sizes, and a printable shopping list you can take to the garden center or order online.

How much soil do you need for a raised bed? Multiply length by width by soil depth to get volume, then add a settling allowance because fresh mixes drop as water and time remove air pockets. Ten percent is a practical default for most vegetable beds, while very fluffy mixes with a lot of bark or coco might need a bit more. Deeper beds for tomatoes or root crops benefit from a sturdy base layer of bulk topsoil blended with rich compost and a small fraction of aeration amendment to keep drainage healthy.

Choosing a soil mix depends on climate, crops, and irrigation. A classic starting point is a balanced mix of topsoil and compost with a light dose of perlite or vermiculite for structure. In wet climates, increase aeration components; in hot, dry summers, add water-holding ingredients like coco coir. Screen out large sticks and stones, pre-moisten the mix before planting, and top dress with compost between seasons to maintain fertility. Keep fertilizers and lime separate from bulk volume calculations because they are applied by rate, not by volume.

The calculator converts every bed into volume, sums the total, and applies your settling percentage to produce a purchase volume. Percentages for your recipe are normalized to 100 if needed, then multiplied by the purchase volume to give per-ingredient volumes. For bag counts, the tool divides each ingredient’s volume by the bag size you entered and rounds up so you do not run short. Use liters for metric bags and cubic feet for imperial bags. If you are filling several identical beds, use the count field to avoid re-typing dimensions.

For accuracy, measure the inside dimensions of the frame and the actual soil depth you plan to fill, not the board height. If your bed has curves or interior dividers, split it into simpler rectangles and add each one as a separate line. You can also set a higher top-off for new cedar beds that will settle after their first season, then dial it back for routine refreshes.