Figuring out how much compost you need can be tricky at times.
And to be honest it’s not always fun doing all the calculations yourself.
And because I know you’re a very busy gardener, I’ve created this compost calculator so you can estimate the quantity of lovely organic compost you need for that new shrub!
You’re welcome 🙂
On top of that, this handy calculator will show you volumes in a variety of units. Imagine someone telling you that you need 10 cubic feet of compost when actually you need to know how many liters you should use!
Yup… I’ve provided the results, in cubic yards, cubic feet, and liters.
I know, I know… you can thank me later…
And if you’re a fan of metric measurements, you’ll find a calculator specially designed for that too!
What more can you ask?
How do you calculate compost volume?
To calculate compost volumes you’ll need a rough idea of the size of the area you want to cover, and the depth of compost you need to apply. The amount of compost required is the product of three things multiplied together: the width, the length and the depth.
Simply put, to calculate the volume you need to multiply three key measurements:
Volume = width x length x depth
The tricky thing about this is you need to keep all of your measurements in the same units. Otherwise the results will be false.
Multiplying feet by inches won’t work. You must multiply feet by feet, or inches by inches.
But most of us measure the size of a garden bed in feet or perhaps meters. But the depth of compost is expressed in inches or centimeters.
For the calculation to be correct you need to turn inches into feet. The magic formula for converting inches to feet is:
Multiply by 0,0833
By integrating this factor of conversion into your calculation your results will be spot on!
Formula for calculating compost volume in feet cubed:
width in feet x length in feet x depth in inches x 0,083 = volume in cubic feet (ft3)
Here’s a quick example. Let’s say you have a garden bed that measures 3 feet wide by 10 feet long and you want to spread 2 inches of compost over the top.
What is the volume of compost you need?
Put everything together and you get:
3 feet x 10 feet x 2 inches x 0,083 = 5 cubic feet
How do I calculate how much compost I need in square yards or square meters?
Of course the same rules hold true if you’re using another unit of measurement. If you prefer cubic yards, or cubic meters, here are some other examples of formulas to use:
Formula for calculating compost volume in yards cubed:
width in yards x length in yards x depth in inches x 0,0031 = volume in cubic yards (yd3)
Formula for calculating compost volume in meters cubed:
width in meters x length in meters x depth in centimeters x 0,01 = volume in cubic meters (m3)
Remember when making your calculations that you’re probably not spreading compost over the whole surface area. Allow for some coverage that won’t receive compost such as pathways. It’s possible you need a bit less compost than you really think!
Understanding compost to soil ratios might seem complicated. I suggest you start by looking at some recommended guidelines for different types of usage in a variety of composting situations. You’ll find a more in-depth guide and some recommendations for typical applications in my article about “How much compost do I need”…
You might only require a ¼ of an inch for an established lawn, or up to 4 inches for very poor quality soil! Once you know the depth of compost required for your type of application, come back to the compost calculator to estimate the quantity you’ll need.
Keep the above formulas handy if you want a rule of thumb for calculating compost quantities. Otherwise, simply plug in some values in the compost calculators to get automatic results.