The No-Nonsense Guide to Compost: Calculation & Application
Don’t Order the Wrong Amount of Dirt
Look, getting a compost delivery is stressful enough. The last thing you want is a mountain of dirt sitting in your driveway for three months because you ordered 5 yards instead of 2. Or worse, coming up short and having to pay a second $100 delivery fee for a “correction” load.
This calculator isn’t just about math; it’s about logistics. Whether you’re trying to fix a patchy lawn or fill a new raised bed, we use industry-standard depths to make sure you get the right amount—down to the bag.
How to Use This Calculator (The Right Way)
Most people mess this up by guessing the depth. Don’t guess. Follow these steps:
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1
Measure Your Area
Walk it off. If your tape measure isn’t long enough, count your paces. An average adult pace is about 3 feet. Close enough for landscaping.
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2
Select “Application Type”
This is the most important button. If you click “Top Dressing Lawn”, we set the depth to 0.25 inches automatically. If you click “Filling Raised Bed”, we set it to 10 inches. Trust the presets.
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3
Check the Price
We’ve loaded average US prices for materials like Mushroom Compost and Manure. It’s an estimate, but it’ll save you from sticker shock when you call the supplier.
Depth Guide: Don’t Smother Your Plants
More is not always better. If you put 2 inches of compost on a lawn, you will kill the grass. Use this cheat sheet:
| Job | Max Depth | Why? |
|---|---|---|
| Lawn Top Dressing | 1/4 inch | Any deeper and you block sunlight to the grass blades. You want the compost to fall between the blades, not bury them. |
| Vegetable Garden (Yearly) | 1 to 2 inches | Just a “top up” to replace what your tomatoes ate last summer. |
| New Raised Bed | 10 inches | You need volume here. But don’t use 100% compost. Mix it 50/50 with topsoil or you’ll have a soup when it rains. |
| Clay Soil Fix | 3 to 4 inches | You need a heavy dose to physically break up the clay particles. Spread it thick, then till it deep (6-8 inches). |
What Type Should I Buy? (Mushroom vs. Manure)
If you call the landscape yard and just ask for “Compost,” they’ll likely send you whatever is cheapest. Be specific.
| Material | The Lowdown | Best For |
|---|---|---|
| Mushroom Compost | It’s the “spent” soil from mushroom farms. Usually cheap and high in calcium. | General Veggies. Great for breaking up clay. |
| Composted Manure | Cow or Chicken poop mixed with straw. High Nitrogen (“Hot”). | Heavy Feeders. Corn, Tomatoes, Pumpkins. Avoid for delicate flowers. |
| Green Waste | Ground up city yard trimmings. Basic, pH neutral. | Lawns. Good for top dressing because it’s usually screened very fine. |
| Topsoil Blend | It’s dirt + compost. It has structure (sand/silt/clay). | Filling Holes. Don’t buy pure compost to fill a hole; it will just shrink away. |
🌱 The “Sniff Test”
Good compost smells like the forest floor after rain. If it smells like ammonia, vinegar, or rotten eggs, it’s not finished “cooking.” Do not buy it. It will burn your plants.
The Science: Fixing Clay vs. Sand
Compost is the universal fixer, but it works differently depending on your native soil.
Fixing Clay Soil (The Brick)
Clay particles are microscopic flat plates that stick together, blocking water and air. When you mix in compost, you physically wedge those plates apart. This creates “pore space” so roots can breathe.
Fixing Sandy Soil (The Sieve)
Sand particles are huge and round. Water runs right through them. Compost acts like a sponge, holding 5x its weight in water. For sandy soil, manure-based compost is often better because it’s “stickier” and adds density.
When to Order? (Spring vs. Fall)
Timing matters almost as much as the material.
- Spring (The “Go” Button): Apply a thin layer (1 inch) just before planting. This warms up the soil darkens the color) and gives seedlings a Nitrogen kick.
- Fall (The “Blanket”): This is actually the best time to go heavy. Apply 2-3 inches after harvest. Winter snow/rain will break it down further, and by Spring, you’ll have perfect soil without lifting a finger.
The Math: Yards vs. Bags
Here’s the math we use. Landscape supply yards speak in Cubic Yards. Home Depot speaks in Cubic Feet.
The Golden Rule
1 Cubic Yard = 27 Cubic Feet
The “Bag” Formula
Yards Needed × 18 = Number of “Big” Bags (1.5cf)
Example A: The Lawn Fix
Scenario: You have a standard 2,000 sq ft suburban lawn. You want a 1/4 inch top dressing.
- Math: 2,000 × (0.25 ÷ 12) = 41.6 Cubic Feet
- In Yards: 41.6 ÷ 27 = 1.5 Yards
- Verdict: Order 2 yards for delivery. It’s way too much to buy in bags (that’s like 30 bags!).
Example B: The Raised Bed
Scenario: Filling a single 4×8 raised bed, 10 inches deep.
- Math: 32 sq ft × (10 ÷ 12) = 26.6 Cubic Feet
- In Yards: It’s basically 1 Yard.
- Verdict: You’re right on the border. If you have a pickup truck, go get a yard. If not, buy ~18 large bags.
Common Questions (FAQ)
How many bags of compost are in a cubic yard?
It depends on the bag size. If you buy the “heavy” bags (1 cubic foot), it’s 27 bags. If you buy the larger bags (1.5 cubic foot) common at big box stores, it’s 18 bags.
What is “Killer Compost”? (Important)
This is a real problem. Some bulk compost is made from hay sprayed with persistent herbicides (like Grazon). It survives the cow’s stomach and the composting process. If you put it on your garden, it will twist and kill your tomatoes and beans. Always ask your supplier: “Is this manure herbicide-free?”
Does compost shrink?
Yes, massively. It’s organic matter, so it decomposes. A raised bed filled 100% with compost can shrink by 50% in a single summer. That’s why you need to mix in topsoil or peat moss for structure that lasts.
What is the difference between “Garden Soil” and “Compost” bags?
Marketing. “Garden Soil” is usually a cheaper pre-mix of topsoil, wood fines, and a little compost. It is a “filler” used for structure. “Compost” is the concentrated nutrient amendment. Never buy Garden Soil to feed your lawn; buy pure Compost.
Can I use compost as mulch?
You can, but be warned: Weeds love compost too. Unlike wood chips which suppress weeds by blocking light, compost provides a perfect nutrient-rich seedbed for them. If you mulch with compost, expect to do some weeding.
Can I use compost instead of fertilizer?
Think of compost as a multivitamin, not a steroid. It improves soil health, but for heavy feeders like corn, you’ll still need granular organic fertilizer.
Compost Calculator
Calculate compost volume and cost for gardens, lawns, and raised beds.
1. Coverage Area
2. Application & Depth
Top Dressing Lawn (0.25″)
3. Material & Cost
Mushroom Compost
Volume (Bulk)
0.0 yd³
Volume (Small)
0.0 ft³
~0 Bags (1.5cf)
Estimated Cost
$0.00
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