Figuring out how much dirt you need isn’t exactly thrilling...until you overfill your truck bed, underfill your garden bed, or overspend by a couple hundred bucks. That’s when the math starts to matter. We’ve been there. 

At Epic Agriculture, we’ve helped countless growers, novices and experts alike, get their beds filled just right, and we can tell you: dialing in the soil volume is one of those quiet little wins that makes a big difference. This isn’t just about math. It’s about building a better foundation for your plants, your time, and your budget.

Key Takeaways

• Calculating soil volume is simple math: Length × Width × Depth (in feet) gives you cubic feet, and dividing by 27 converts it to cubic yards.
• Ideal soil depths vary, 12–18" for shallow crops, 18–24" for medium ones, and 24"+ for deep-rooted veggies like tomatoes and carrots.
• Always round up slightly when ordering soil to account for settling, compaction, and water loss over time.
• A strong raised bed soil mix includes 60% topsoil, 30% compost, and 10% amendments like perlite or sand.
• Overfilling initially and watering deeply helps prevent mid-season volume loss and avoids emergency soil runs.
• Epic Agriculture offers raised beds, soil, and amendments designed to help you grow smarter and avoid costly dirt miscalculations.

Why Soil Volume Matters in Raised Beds

Here’s the deal, soil volume isn’t just a number, it’s a decision that affects everything else: plant health, water drainage, root development, even your back when it’s time to shovel. Add too little soil and your plants might struggle with shallow roots, dry out too fast, or simply not thrive. 

Add too much, and you’re either wasting good money or watching it spill out onto the patio with the first heavy rain. But when the volume is right? Your garden works with you, not against you. It holds moisture where it should, gives your crops room to stretch their legs (or roots), and just feels...settled. Like a well-made bed.

Step-by-Step: How to Calculate Soil Volume

We’re not going to make you pull out graph paper, but this is a spot where a little precision pays off. Let’s break it down in three quick steps.

1. Measure Your Raised Bed Dimensions

Start by grabbing your tape measure and jotting down three numbers: length, width, and depth, all in feet. Raised beds often come in familiar sizes like 4x4 or 4x8, but we always suggest measuring anyway. 

Custom builds, stacked heights, and in-ground hybrids can throw off assumptions. Got depth listed in inches? No problem. Just divide by 12. For quick reference:

• 6" = 0.5 feet
• 10" = 0.83 feet
• 12" = 1 foot

Precision here helps avoid miscalculations later, especially if you're ordering soil in bulk.

2. Multiply to Find Cubic Feet

Now for the basic formula: Length × Width × Depth = Total Cubic Feet

So, let’s say your bed is 4 feet wide, 8 feet long, and 1 foot deep: 4 × 8 × 1 = 32 cubic feet

Simple enough, but don’t walk away just yet, we’re not done.

3. Convert to Cubic Yards (If Needed)

If you’re buying soil in bags, they’re usually labeled in cubic feet. But for bulk soil (like when you call a local supplier), you’ll need cubic yards. One cubic yard = 27 cubic feet. So in our example: 32 ÷ 27 = 1.18 cubic yards

And here’s our honest tip: round up a little. Soil settles. Beds settle. Life happens. It’s better to have a small leftover pile than be half a wheelbarrow short on a Sunday afternoon when the garden center’s already closed.

Ideal Soil Depths Based on Plant Types

Not all plants have the same needs, and neither do gardeners. Some of us are growing salad greens for the family, others are cultivating prize-winning heirloom tomatoes or deep-rooted carrots that look like they belong in a Tolkien novel. Whatever your goals, your soil depth should match the crop.

Shallow Rooted Crops

These are your lettuce, spinach, arugula, and herb varieties. If you're short on soil, short on budget, or just starting out, they’re a forgiving bunch.

• Ideal depth: 12–18 inches
• Great for shallow beds or vertical setups.

Medium Rooted Crops

Think beans, peas, peppers, plants that aren’t divas but still want a little room.

• Ideal depth: 18–24 inches
• This range gives most garden favorites the root space they need for consistent growth and yield.

Deep Rooted Crops

Tomatoes, carrots, potatoes, these heavy hitters need real depth to do their thing.

• Ideal depth: 24 inches or more
• If you want fewer cracked carrots and bigger tomato harvests, don’t skimp here.

That said, you don’t always have to build 24” deep beds right off the bat. You can create layered systems (like hugelkultur) or grow these crops in containers or grow bags specifically designed for depth. There’s always a workaround if space or cost is an issue.

How Much Dirt Will You Actually Need?

Let’s start with the basics. To figure out how much soil you need, multiply your raised bed’s length, width, and depth (all in feet). That gives you the total cubic feet. If you’re buying in bulk, divide that number by 27 to convert it to cubic yards. Easy math, but here’s where most folks trip up.

Soil settles. Compost breaks down. Water compacts everything. What looks like a full bed in April can sink by a few inches by mid-May, especially after a couple of solid rains. We’ve seen it time and time again. 

So, if you're aiming for long-term consistency, plan ahead. Slightly overfill the bed, yes, even mound it a bit, and water deeply. Once it compresses, top it off again. It’s much easier (and cheaper) to do this up front than scramble to fill gaps in the middle of your season.

Recommended Soil Mix for Raised Beds

Now, let’s talk quality, not just quantity. What you fill your raised bed with matters. A well-balanced mix supports your plants from root to fruit. Our go-to soil recipe, refined over years and dozens of test beds, is a tried-and-true formula:

• 60% Topsoil: This gives your bed structure and holds everything together. It’s the meat and potatoes of your soil mix.
• 30% Compost: Nutrient-rich and microbially active, compost does the heavy lifting when it comes to feeding your plants naturally.
• 10% Amendments: Depending on your needs, this can include perlite for aeration, vermiculite for moisture retention, or coarse sand for drainage. Don’t skip this, it’s your soil’s “tuning knob.”

We know everyone’s local supply is different. Maybe your nursery has killer compost but lackluster topsoil. Maybe you're working on a budget and need to make use of what you have. That’s fine, just aim to get close to this balance, and adjust based on what you’re growing and your climate.

Build Your Raised Garden Bed Right with Epic Agriculture

At Epic Agriculture, we know that a raised garden bed is only as good as what you fill it with, and we’ve got everything you need to do it right from day one. From durable raised garden beds to premium soil, compost, and essential amendments like perlite and vermiculite, we make it easy to build a thriving foundation.

Whether you're starting your first bed or scaling up your garden space, our growing supplies are curated to help you grow smarter, not harder. Ready to fill your bed with purpose? Explore our raised bed solutions and start growing with confidence.

Recap: How Much Dirt You Need For Your Raised Garden Bed

At the end of the day, soil isn’t just dirt, it’s the foundation of your entire garden. And when you take the time to measure correctly, fill smart, and build a mix that actually supports plant health, you’re stacking the odds in your favor. You don’t need to be perfect, just thoughtful.

So measure once, fill it right, and let the growing begin. A few extra inches of soil today could be the difference between a ho-hum harvest and a season that overflows with herbs, veggies, and satisfaction. And if you need a new raised garden bed or even soil, come check out our selection at Epic Agriculture and get it delivered right to your door.