Spring is underway, and chances are youâ€™re busy preparing your garden for planting season. If youâ€™re keen to expand this year and grow more of your own food, youâ€™re probably thinking about building raised garden beds. But building beds is only half the battleâ€”the next step is to fill them with quality soil.
Whether youâ€™re pulling the soil from your own compost pile or sourcing it from another location, youâ€™ll need to calculate the volume of soil you need. This goes double if you plan to add amendments to the soil.
To make sure you donâ€™t apply too much (or too little), you need to determine the volume of soil and distribute the amendment accordingly.
Grab Your Calculator
Fortunately, itâ€™s easy to calculate how much soil you need to fill a raised bed. Yes, it involves a little algebra, but thereâ€™s no need to run screaming in another direction! This isnâ€™t the imposingly complicated and theoretical algebra you learned in high school.
Hereâ€™s the magic formula you need to calculate soil volume in raised garden beds:
W x L x D = Vft3
Confused? Thereâ€™s no need to beâ€”this is really just a straightforward multiplication problem. It only looks complicated because we havenâ€™t punched in the real numbers yet.
Break It Down
Letâ€™s explain the variables in the equation:
W = the width of your garden bed, in feet
L = the length of your garden bed, in feet
D = the depth of your garden bed, in fee.
V = the volume, in cubic feet, of soil you will need to fill the bed
Now, letâ€™s replace the variables with numbers. Suppose your garden bed measures 3 feet wide by 8 feet long, and you want to fill the bed 12 inches (1 foot) deep. Suddenly, the equation looks more like a real math problem:
3 x 8 x 1 = 24ft3
If you want to fill the bed 2 feet deep, youâ€™ll need twice as much soil. This is reflected in the updated equation:
3 x 8 x 2 = 48ft3
Change It Up
Now letâ€™s change up the numbers significantly. Suppose your bed measures 4 feet wide by 10 feet long, but you only wish to fill it 8 inches (0.67 feet) deep. So long as you remember to convert inches into feet, the formula continues to work just fine.
4 x 10 x 0.67 = 26.8ft3
If you would like to measure using a unit other than feet, feel free to do so! Inches, yards, centimeters, metersâ€”all can be used with accurate results, so long as you donâ€™t mix and match different units of measurement:
Meters: 1 x 3 x 0.5 = 1.5m3
Inches: 12 x 36 x 6 = 2,592in3
This same formula can be used to calculate the carrying capacity of a wagon or trailer. Suppose you plan to haul compost to your garden in a wagon measuring 4 feet wide by 9 feet long and 2 feet deep. If you fill this wagon to the brim (and level off the compost so itâ€™s not heaping above the sides of the wagon), youâ€™ll be hauling exactly 72ft3 of soilâ€”enough to fill three beds measuring 3 feet wide by 8 feet long and 1 foot deep (containing 24ft3 of soil).
Congratulations! You have successfully calculated how much soil you need to fill your raised garden beds. Happy growing season!