Raised Bed Soil Calculator

Calculator Inputs

Bed shape

Length, side, or diameter

Width or oval diameter

Length unit

Target bed depth

Existing filled depth

Depth unit

Number of beds

Final fill percent

Settling allowance percent

Waste allowance percent

Soil bag size

Bag size unit

Price per bag

Bulk price per cubic yard

Topsoil percent

Compost percent

Coir or peat percent

Aeration material percent

Amendment cups per cubic foot

Example Data Table

Bed size	Depth	Allowance	Approximate loose soil	Common use
4 ft × 8 ft	12 in	10% settling, 5% waste	37.33 cu ft	Vegetables
3 ft × 6 ft	10 in	10% settling, 5% waste	17.50 cu ft	Herbs and greens
Round 4 ft diameter	14 in	10% settling, 5% waste	17.10 cu ft	Flowers
2 ft × 10 ft	8 in	10% settling, 5% waste	15.56 cu ft	Narrow border bed

Formula Used

Rectangle area: Area = Length × Width.

Square area: Area = Side × Side.

Round area: Area = π × Radius².

Oval area: Area = π × Length radius × Width radius.

Target depth: Final depth = Bed depth × Fill percent.

Additional depth: Additional depth = Final depth − Existing filled depth.

Raw volume: Raw volume = Area × Additional depth × Bed count.

Loose soil: Loose soil = Raw volume ÷ (1 − Settling percent) × (1 + Waste percent).

Bag count: Bags = Ceiling value of Loose soil ÷ Bag size.

How to Use This Calculator

Select the raised bed shape.
Enter inside length and width measurements.
Enter the target soil depth.
Add existing filled depth for top-up jobs.
Set the number of beds.
Add settling and waste allowances.
Enter bag size and price details.
Adjust mix percentages for your soil recipe.
Press calculate to view soil, bags, cost, and mix amounts.
Use the CSV or PDF button to save the result.

Understanding Raised Bed Soil Needs

A raised bed works best when roots have enough loose soil. The bed depth controls that volume. The surface size controls planting area. This calculator joins those values and gives a clear filling plan. It helps before buying bags or ordering bulk soil.

Why Depth Matters

Most herbs grow well in shallow beds. Leafy greens need moderate depth. Tomatoes, peppers, carrots, and potatoes need more room. Extra depth also holds more water. It supports stronger roots during hot weather. A deeper bed costs more to fill, so planning matters.

Choosing a Mix

Good raised bed soil is not plain garden dirt. It should drain, hold moisture, and feed plants. Many gardeners use topsoil with compost. They may add peat, coco coir, perlite, or bark fines. Compost adds nutrients. Mineral soil adds body. Light materials improve air space.

Allowances and Settling

Fresh soil settles after watering. Bagged mixes also compress during transport. A bed filled to the rim may drop later. The allowance fields help cover this loss. A waste allowance also protects against uneven ground, spilled material, or small measuring errors.

Bags or Bulk Soil

Small beds are easy to fill with bags. Large beds often cost less with bulk soil. The calculator shows both paths. Bag count is rounded up. This prevents a shortage near the end. Bulk volume is shown in cubic yards, which suppliers commonly use.

Practical Buying Tips

Measure inside bed dimensions. Boards take space, so outside dimensions can overstate volume. Confirm bag size before buying. Some bags are sold in liters. Others use cubic feet. Mix percentages should total near one hundred. The calculator normalizes them when needed.

Using Results in the Garden

Use the result as a planning guide. Level the bed first. Add coarse material only when it supports drainage. Avoid filling deep beds with pure compost. It can shrink fast. Water the mix in layers. Check the final height after settling. Add mulch after planting to reduce moisture loss.

Seasonal Adjustments

Spring beds may need extra compost after winter rain. Summer beds may need more mulch and water. Fall beds can use leaf mold or aged manure. Always match the mix to crop needs and drainage well.

FAQs

How much soil do I need for a raised bed?

Measure the inside length, width, and depth. Multiply them to get volume. Then add settling and waste allowances. This calculator does those steps and shows bags, liters, gallons, and cubic yards.

Should I measure inside or outside dimensions?

Use inside dimensions. Wood, blocks, or metal sides reduce usable growing space. Outside dimensions can make the soil estimate too high, especially with thick boards or stone walls.

What depth is best for vegetables?

Many vegetables grow well in 10 to 12 inches. Root crops and large plants may need 14 to 18 inches. Deeper beds store more moisture and support larger roots.

Why does the calculator add settling allowance?

Loose soil settles after watering and planting. Compost and bagged mixes may compress more. A settling allowance helps you buy enough material to keep the final bed height useful.

Can I use only compost in a raised bed?

Pure compost can shrink quickly and may hold too much moisture. A balanced mix usually works better. Use compost with mineral soil and aeration material for structure.

How are soil bags calculated?

The calculator converts bag size to cubic feet. It divides loose soil volume by that bag size. The answer is rounded up, because partial bags are not usually sold.

When should I order bulk soil?

Bulk soil is useful for larger beds or many beds. It may cost less per cubic foot. Check delivery fees, minimum order size, and soil quality before buying.

Can this calculator handle top-up soil?

Yes. Enter the existing filled depth. The calculator subtracts it from the target fill depth. It then estimates only the extra soil needed.