Soil Calculator Defined: How to Calculate Soil for a Garden Bed

Soil is a landscape material and prominent medium in which plants of all varieties grow. There are many different types of soil (clay soil, sandy soil, loam soil, etc.) often combined in a single mixture. Many soil mixes come infused with additional amendments and beneficial microorganisms to aid in moisture retention and provide nutritional sustenance for your plants.

A soil or dirt calculator is an online calculator pre-programmed to take the inputs necessary to discover how much soil should fill in a specific area. It does so by calculating soil volume (multiplying the length, width, and depth of a garden bed) for a given garden and then dividing that number by the cubic feet of soil available in a specific bag of soil.

For instance, a lengthwise yard of topsoil that is two yards widthwise with a garden soil depth of one yard equals two cubic yards of soil. If one yard of soil is available in each bag of soil you plan to purchase, you will need two bags of soil total to lay everything necessary. Even though most soil calculator designers likely have garden soil or potting soil in mind, you can use their digital tools to perform similar calculations for soilless potting mix (peat moss, perlite, etc.), paver, and other materials.

Soil volume is a cubic measurement you get from multiplying the height, width, and depth of a given garden bed together. Depending on the specific soil calculator you use, you might calculate the soil volume in a metric of cubic inches, cubic meters, or even cubic yards of soil. But cubic feet is perhaps the most useful, given pre-packaged bags of soil often advertise their wares in cubic feet. You can always do conversions to transition your calculations to another metric.

Although there are plenty of automated options online, you can also perform your own soil calculations manually. If you’d prefer to take a more DIY approach to soil calculation, try these five steps:

1. 1. Decide where to measure. Choose an area of your garden where you would like to place more soil. Keep in mind that you want about twelve to eighteen inches of depth for your plants’ roots to stretch downward. If you’re using a raised garden bed for container gardening, you should still factor in the depth available beneath it in your native soil. If you’re forgoing a raised bed, take into account how much depth you have in your native soil already, too. This ensures you won’t use more than necessary.
2. 2. Find the area. Use a tape measure, ruler, or smart device to take the length and width measurements. Multiply the length times the width to determine the square footage. You can do so by hand, on a typical calculator, or access an online area calculator that already includes these input fields.
3. 3. Multiply by the depth. Store the square feet provided by the total area and then take a measurement for the depth you require for your soil project. Multiply the total area times the depth to determine the cubic feet of soil (or a different cubic measurement). Consider using an online volume calculator to automate this process as much as possible.
4. 4. Divide by the amount of soil in a bag. Most bags of soil will advertise the number of cubic feet they provide. Dividing the total volume by the cubic feet in a single bag of soil will determine the number of bags necessary to provide the right amount of soil.
5. 5. Lay the soil. Now that you have the total volume of soil necessary, it’s time to lay it down in your garden. Fill dirt into your garden bed or simply lay it atop your native soil. Mulch the soil with organic matter to encourage a nutritious environment for your plants. Consult any relevant gardening tips for the plants you plan to place in your new soil.

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