Raised Bed Soil Calculator: How Much Soil Do I Need?

How to Use the Raised Bed Soil Calculator

The calculator gives you two easy ways to estimate your soil requirements.

Calculating Soil for a Birdies Raised Garden Bed

If you already know which Birdies bed you would like, use one of the built-in product options:

1. Select Choose a Garden Bed Model.
2. Choose your Birdies bed height.
3. Select Medium, Large, Jumbo or Round.
4. Choose your preferred bed configuration.
5. Select Calculate Soil Volume.

The Birdies presets use the dimensions and effective capacity of the selected garden bed. There is no need to measure the bed or convert the result yourself.

For planning and ordering purposes, calculate enough soil to fill the bed to the top. Organic-based soil mixes usually settle after filling and watering, and the bed may need to be topped up during the first two to three growing seasons.

Still deciding which bed size or configuration will suit your garden? Use the Birdies Garden Planner to place different Birdies beds on your property and compare your options before purchasing.

Calculating Soil for a Custom Raised Bed

Select Enter Dimensions if you want to calculate the soil volume for another rectangular or round raised bed.

Choose imperial or metric measurements and enter the bed's stated length, width and full height. The result does not need to account for every curve, brace or small variation in the bed. It is a practical estimate for ordering soil, and natural settling is likely to have a greater effect than minor differences in measurements.

Understanding Your Soil Calculator Result

The calculator displays the same estimated soil volume in four useful units:

• Litres are helpful when purchasing metric bags of soil or compost.
• Cubic metres are commonly used for larger bulk orders in metric markets.
• Cubic feet are helpful when purchasing bagged soil in the United States.
• Cubic yards are commonly used by US bulk landscape suppliers.

Soil is usually sold in fixed bag sizes or bulk-delivery increments. Once you have your estimate, round up to the next quantity your supplier can provide.

Remember that organic-based mixes naturally settle. Filling the bed to the top at the start gives the mix room to settle, but you should still expect to add more soil or compost as the level drops over the first two to three growing seasons.

If you are planning several Birdies beds, the Garden Planner can make this step much easier. As you place beds into your design, it creates a combined soil estimate and shopping summary for the entire plan.

Go Beyond One Bed With the Birdies Garden Planner

The soil calculator is ideal when you want a quick answer for a single raised bed. If you are designing a larger garden or comparing several possible layouts, the Birdies Garden Planner helps you plan the whole project in one place.

Plan on Your Actual Property

Start with a satellite view of your property so you can see the available space around your home, shed, fence, driveway and existing garden.

You can mark the area you want to work with and switch to a clean planning view whenever you need a simpler canvas.

Add Beds, Structures and Boundaries

Drag and drop Birdies raised garden beds into your plan and arrange them until the garden feels right.

You can also add houses, sheds, walls, paths and custom boundaries. This helps you check that your beds fit comfortably and that you have allowed practical access around them.

Leave at least enough space between beds and structures for a garden cart or wheelbarrow. A little extra room can make filling, planting, harvesting and topping up your beds much easier.

Compare Birdies Products and Colours

Try different Birdies bed sizes, heights, configurations and colours before making your final choice.

Seeing the products together in your planned garden can make it easier to decide whether you prefer one large growing area, several smaller beds or a combination of shapes and sizes.

Birdies currently offers 15-inch and 29-inch raised beds, with a new 20-inch height coming soon. You can explore the full range of Birdies raised garden beds while building your plan.

Check Sunlight and Shade

The planner allows you to preview how sunlight and shade may move across your garden at different times of the day and year.

This can help you choose more suitable positions for your raised beds and consider which plants may be happiest in each part of the garden.

See Your Total Soil Estimate

As you add Birdies beds, the planner estimates the soil volume required for your chosen layout.

This is especially useful when planning multiple raised beds because you can see an estimated total without calculating each bed separately and adding all the figures yourself.

Add Your Plan Straight to Your Cart

Once you are happy with your layout, review the products and estimated total in your shopping summary.

You can then add the Birdies products from your plan straight to your shopping cart, creating a much simpler journey from your first garden idea to placing your order.

Save Your Garden Plan

You can start a Quick Plan as a guest without creating an account.

If you would like to save your work and return to it later, log in or register before creating your plan. This is helpful if you want to compare different layouts, discuss the design with someone else or build your garden in stages.

How Is Raised Bed Soil Volume Calculated?

For a rectangular raised bed, the basic calculation is:

Length × width × bed height = soil volume

All measurements must use the same unit. If your length and width are measured in feet but the bed height is measured in inches, divide the height by 12 before completing the calculation.

For a round raised bed, the formula is:

Pi × radius² × bed height = soil volume

The radius is half the diameter of the bed.

The Birdies calculator handles these formulas and unit conversions for you.

How Much Soil Does a 4 × 8 ft Raised Bed Need?

The amount depends on the full height of the bed. For example, a 4 × 8 ft bed that is 15 inches high requires:

4 × 8 × 1.25 = 40 cubic feet of soil

One cubic yard contains 27 cubic feet, so:

40 ÷ 27 = approximately 1.48 cubic yards

This is the estimated amount required to fill the bed to the top. Because organic-based soil mixes settle after watering and over time, expect the level to drop and plan to top it up during the first two to three growing seasons.

Should I Fill My Raised Garden Bed to the Top?

Yes. Birdies recommends calculating and ordering enough soil to fill the raised bed to the top.

Organic-based soil mixes contain materials that continue to break down and settle after the bed has been filled. Starting at the full bed height helps account for this early drop in soil level.

Mulch can be mounded slightly above the top rim of the bed. It will usually settle and drop fairly quickly after watering and exposure to the weather.

Check the soil level from time to time and top the bed up with suitable soil or compost as required. This is particularly important during the first two to three growing seasons.

How Deep Should the Soil Be in a Raised Garden Bed?

For calculating how much soil to order, use the full height of your raised bed rather than reducing the depth based on a general planting recommendation.

The full soil profile provides growing space for a wide variety of vegetables, herbs, flowers and deeper-rooted crops. It also allows for the settling that naturally occurs in organic-based mixes.

Birdies raised garden beds can be installed in a variety of garden settings, including over soil, lawn and suitable hard surfaces when Birdies' current installation guidance is followed.

If you are choosing a bed height, compare Birdies' 15-inch raised garden beds and 29-inch raised garden beds. A new 20-inch option is also coming soon.

You can place different bed heights into the Birdies Garden Planner to see how they work within your proposed layout.

What Is the Best Soil for a Raised Garden Bed?

A good raised bed soil mix should hold enough moisture for your plants while still allowing air and excess water to move through it.

The soil should feel loose and workable rather than heavy, compacted or waterlogged.

There is no single mixture that suits every garden, climate and crop. A useful starting point is a blend of quality screened topsoil and mature compost.

Iowa State University Extension suggests approximately 70% topsoil and 30% compost as one option for raised garden beds.

A reputable local supplier may also offer a prepared mix designed specifically for raised vegetable gardens. Ask what the mix contains, especially if manure-based compost is included.

Compost is valuable, but more is not always better. The University of Minnesota Extension explains that excessive compost or manure can sometimes create nutrient and salt problems.

Filling a 15-Inch Birdies Raised Garden Bed

A 15-inch Birdies bed provides a practical growing depth for vegetables, herbs, flowers and many root crops.

Fill the entire bed to the top with a quality, complete raised bed soil mix. Organic-based mixes will settle as they are watered and the organic material breaks down, so expect to top up the bed during the first two to three growing seasons.

Mulch can be mounded above the rim when first applied. It should settle quickly while helping the soil retain moisture and feeding the soil as it breaks down.

Filling a 20-Inch Birdies Raised Garden Bed

Birdies has a new 20-inch raised garden bed coming soon. It will provide a useful middle option for gardeners who want more height and soil capacity than a 15-inch bed without moving up to the full height of a 29-inch bed.

When the range becomes available, use the calculator preset for your chosen configuration and fill the bed to the top. As with other organic-based soil mixes, expect some settling and plan to top up the bed over the first two to three growing seasons.

Filling a 29-Inch Birdies Raised Garden Bed

A 29-inch Birdies bed provides a comfortable working height and considerably more total capacity.

You can fill the entire bed with a quality raised bed mix. You can also use the hügelkultur method to reduce the amount of premium soil needed while making use of suitable organic material.

For this method, the bottom section of the bed can be filled with clean general garden waste or untreated timber logs. Add quality growing soil through the upper section and fill the bed to the top.

Use only clean, untreated materials. Avoid treated timber, contaminated soil, diseased plant material and anything likely to introduce persistent weeds or unwanted chemicals.

The woody and organic layers will break down and settle over time. Check the level regularly and expect to add more soil or compost during the first two to three growing seasons. You can learn more about the principles behind hügelkultur from Oklahoma State University Extension.

Should I Buy Raised Bed Soil in Bags or in Bulk?

Bagged soil is convenient for smaller projects, occasional top-ups and gardens where access is difficult.

The Birdies Elevated Planter is specifically designed to be filled with bagged potting mix, making it a convenient option for patios, balconies and smaller growing spaces.

Check the volume printed on each bag rather than relying on its weight. Moisture levels and ingredients can make two bags of the same volume weigh very different amounts.

For one large bed or several raised beds, ordering soil in bulk may save money, packaging and a great deal of carrying.

Before arranging a delivery, ask your supplier:

• Is the soil sold by the cubic yard or cubic metre?
• What ingredients are included in the mix?
• Is there a minimum order?
• Is there a separate delivery fee?
• Where can the soil be unloaded?
• Can you reach your beds with a garden cart or wheelbarrow from the delivery point?

It is much easier to answer these questions before a truck full of soil arrives at your gate.

Common Raised Bed Soil Calculation Mistakes

Chasing Unnecessary Measurement Precision

The calculator provides a practical estimate for ordering soil. For a custom bed, use its stated length, width and full height. Small differences caused by rounded corners, braces or minor measurement variations are usually less important than the natural settling of an organic-based soil mix.

Reducing the Fill Height

Calculate enough soil to fill the bed to the top. Organic-based soil will settle after filling and watering, and the level may continue to drop as organic material breaks down over the first two to three growing seasons.

Mulch can be mounded above the rim and will usually settle fairly quickly.

Forgetting About Every Bed

The soil calculator estimates one bed at a time.

For several identical beds, multiply the result by the number of beds. For different bed sizes, calculate each one separately and add the results together.

Alternatively, create the complete layout in the Birdies Garden Planner to see the estimated total soil requirement across all the Birdies beds in your design.

Forgetting About Access Around the Beds

A bed may technically fit into a space while leaving too little room to garden comfortably.

Allow at least enough space for a garden cart or wheelbarrow between beds, structures and boundaries. The Birdies Garden Planner helps you visualise the full layout before you begin moving soil or assembling beds.

Purchasing Soil by Weight

Use the volume shown on the soil bag. Weight can change depending on the ingredients and moisture content.

Filling the Bed With Compost Alone

Compost is a useful soil amendment, but it is not automatically a complete growing medium. Too much compost may create nutrient, salt or drainage problems.

Calculate the Soil, Then Plan the Garden

The soil calculator helps you understand how much soil one raised bed may need. The Birdies Garden Planner takes you further by helping you see how the entire garden could work before you purchase anything.

Place Birdies products on your actual property, compare layouts, explore sunlight and shade, estimate the total amount of soil required and turn your finished plan into a shopping cart.

Whether you are adding one bed or transforming your entire backyard, a little planning now can save time, effort and uncertainty later.