Introduction
How many bags do I need? How many cubic yards is my bed? How deep should it be, and how much extra should I order for settling? These are the questions every raised-bed builder asks, and every one of them has a concrete numerical answer. The Garden Soil Calculator computes volume, bag counts, and weight from your dimensions — the answers below explain the reasoning so you can trust the numbers.
This FAQ covers the twelve most-asked garden soil questions, with worked examples in both imperial and metric units. If you need the full background on any answer, the linked guides go deeper.
Garden Soil FAQ
How many bags of garden soil do I need for a 4×8 raised bed?
At 12 inches deep, the bed holds 4 × 8 × 1 = 32 ft³. Divide by the 1.5 ft³ bag size: 32 ÷ 1.5 = 21.3, so buy 22 bags — 25 if you add 15% for settling. At 8 inches deep it is 21.3 ft³, so 15 bags (17 with settling allowance). See the formula guide for the full calculation.
How many cubic yards of soil is my raised bed?
Divide cubic feet by 27. A 4 × 8 bed at 12 inches is 32 ft³ = 1.19 yd³; at 8 inches it is 21.3 ft³ = 0.79 yd³. A 4 × 4 bed at 12 inches is 16 ft³ = 0.59 yd³. Order bulk in rounded increments — 1.5 yd³ covers the first example with settling included.
What is the difference between garden soil, topsoil, and potting mix?
Garden soil is a blend of topsoil, compost, and amendments designed for beds. Topsoil is plain screened soil — cheaper but variable and often low in organic matter. Potting mix is soilless and engineered for containers; it dries too fast for large beds. The material guide compares all three in detail.
How deep should a raised bed be?
Eight to twelve inches (20–30 cm) suits most vegetables, herbs, and flowers. Go 12 inches (30 cm) or deeper for root vegetables and for beds over concrete or compacted ground. Shallower than 6 inches (15 cm) limits you to herbs and leafy greens.
How much does soil settle, and how much extra should I order?
Fresh soil settles 10–20% in the first season. Add 10–15% to your calculated volume when ordering — for a 32 ft³ bed that means ordering ~36 ft³ (1.35 yd³ or 25 bags). Mound the bed 1–2 inches above the frame and top-dress with compost in fall.
Can I fill a raised bed with 100% compost?
No. Compost continues to decompose and collapse, holds excessive water, and can tie up nutrients. Use a garden soil blend or roughly a 50/50 mix of topsoil and compost.
How do I convert my answer to metric?
A 1.22 m × 2.44 m bed at 0.30 m deep gives 0.89 m³ (1.22 × 2.44 × 0.30). Converting the imperial answer instead — 1.19 yd³ × 0.7646 = 0.91 m³ — differs only by rounding. For ordering, convert the final volume, not each dimension.
Is bulk or bagged soil cheaper?
Bulk is cheaper per cubic yard — typically $30–60/yd³ versus $72–144/yd³ equivalent for bagged. But delivery fees ($40–100) can erase the advantage on a single small bed. Bulk wins clearly at two beds and up. Full comparison in the cost guide.
How do I amend poor native soil instead of building a bed?
Spread 2–3 inches (5–7.5 cm) of compost over the area and work it into the top 6–8 inches (15–20 cm) with a fork or tiller. For a 10 × 10 ft area, 2.5 inches of compost is 10 × 10 × 0.208 = 20.8 ft³, or about 0.77 yd³.
What lumber is safe for raised beds with edibles?
Untreated cedar or redwood, composite lumber, and modern ACQ/CA-treated lumber are all commonly used. Avoid creosote-treated ties and old CCA-treated lumber near food crops. Many gardeners line modern treated beds as a precaution — details in the DIY vs. pro guide.
How heavy is the soil I am ordering?
Moist garden soil weighs roughly 75–100 lb/ft³ (1.0–1.35 tons/yd³). A 32 ft³ bed is about 2,400–3,200 lb — plan on ~1.5 tons for trailer and driveway purposes.
Do I need to test drainage before filling?
Yes if the bed sits on native ground. Dig a 12-inch hole, fill with water twice, and time the second drain — longer than ~4 hours means poor drainage. Build taller, improve the site, or relocate.
Should I line the bottom of my raised bed?
Usually no. An open bottom lets excess water drain and allows roots and earthworms to move between the bed and the subsoil. The exception is beds over contaminated ground or aggressive perennial weeds (like bindweed), where a permeable landscape fabric barrier is justified. Never use impermeable plastic on the bottom — it creates the bathtub effect described in the common mistakes guide.
How long does garden soil last before it needs replacing?
Indefinitely, with maintenance. Annual top-dressing of 1–2 inches of compost plus mulch keeps a bed productive year after year. Full replacement is only needed for contamination or severe compaction — growers who replace soil every few years are usually compensating for skipped upkeep.
Can I reuse soil from an old bed?
Yes, with refreshing. Screen out roots and debris, blend in 25–30% fresh compost by volume, and check for persistent weeds or disease issues from the previous planting. Reused soil that grew tomatoes with blight should not grow tomatoes again immediately — rotate crops regardless of whether the soil is new or reused.
Related Guides
- Complete Guide — the full walkthrough behind these answers.
- Formula Explained — every calculation shown step by step.
- Estimating Guide — irregular beds, planters, and multi-bed totals.
- Cost Guide — bulk vs. bagged pricing in detail.
- Material Guide — garden soil vs. topsoil vs. potting mix.
Get Your Number
Turn these answers into your exact order with the Garden Soil Calculator — enter your dimensions, add the settling allowance, and compare bulk and bagged pricing.
Disclaimer: Calculator results are planning estimates based on the dimensions you enter. Actual material requirements vary with product density, moisture content, and settling. Verify quantities with your supplier and consult a licensed professional for drainage or code-related decisions.
