Garden

Soil Calculator

Building a 4x8 raised bed and trying to figure out if 10 bags of soil from Lowe's is enough or way too much? Soil is sold in cubic feet (bags, typically 1-3 cu ft each) and cubic yards (bulk delivery). A 4x8 raised bed 12" deep needs 32 cubic feet of soil — that's about 21 bags of 1.5 cu ft. Or 1.2 cubic yards from a landscape supplier. This calculator runs the math for any rectangular raised bed or planter and tells you cubic feet, cubic yards, and how many bags of various sizes you'd need. Plus a few preset buttons for common raised bed sizes.

Enter bed dimensions.

Bag vs bulk: cost crossover

Soil pricing 2025 ballpark:

Bagged topsoil: $4-7 per 1 cu ft bag = $110-190 per cubic yard equivalent
Bagged garden soil / raised bed mix: $5-10 per 1.5 cu ft bag = $90-180 per cubic yard
Bulk topsoil delivered: $35-60 per cubic yard
Bulk garden soil / 50-50 mix delivered: $50-90 per cubic yard
Bulk premium mix (Mel's Mix, etc.) delivered: $75-150 per cubic yard

Crossover point: above about 1-1.5 cubic yards (27-40 cu ft = 18-27 bags of 1.5 cu ft), bulk delivery is dramatically cheaper. Below that, bagging is more convenient.

Worked example: 4x8 raised bed, 12" deep. Volume = 4 × 8 × 1 = 32 cu ft = 1.18 cubic yards. Bagged: 22 bags of 1.5 cu ft at $6 each = $132. Bulk delivered: 1.5 yards (rounded up) at $50/yard = $75 + $30 delivery = $105. Bulk wins by ~$30 plus you handle the soil at the truck instead of carrying 22 bags.

Raised bed soil mix recipes

Mel's Mix (Square Foot Gardening): 1/3 compost, 1/3 peat moss, 1/3 vermiculite. Lightweight, drains well, no native soil. Great for first-fill of new beds.

Standard raised bed mix: 50% topsoil, 30% compost, 20% aeration (perlite or coarse sand). Cheaper than Mel's, almost as productive.

Lasagna fill (bottom 1/2 of deep beds): alternating layers of brown organic matter (cardboard, straw, dry leaves) and green organic matter (grass clippings, kitchen scraps). Saves money on filling deep beds; decomposes into rich soil over 1-2 years.

Topping soil for established beds (year 2+): 100% compost or 50/50 compost/topsoil to refresh nutrients and replace settled volume.

How to use this calculator

Length and width in feet.
Depth in inches.
Bag size: 1.5 cu ft is most common.
Output: cubic yards, cubic feet, bag count.
Preset buttons: load 4x4, 4x8, 2x8 narrow, or 4x12 deep raised bed dimensions.

Common scenarios

4x8 raised bed, 12" deep. 32 cu ft = 1.2 cubic yards = 22 bags of 1.5 cu ft. Bulk: ~$105 delivered. Bagged: ~$132 carried home.

4x12 deep raised bed, 24" deep (for root vegetables). 96 cu ft = 3.6 cubic yards. Bulk delivery is essential at this scale — 64 bags would be brutal to handle. Consider lasagna filling the bottom 12" to reduce premium soil cost.

Small balcony container collection: 5 pots averaging 14" diameter, 12" deep. Each pot: π × 7² × 12 = 1,847 cu in = 1.07 cu ft. 5 pots = 5.4 cu ft = 4 bags of 1.5 cu ft. Easily managed bagged.

FAQ

Raised bed mix vs garden soil vs topsoil? +

Raised bed mix (premium): light, well-draining, balanced compost — ready to plant. Garden soil (mid-grade): denser, lower compost content, may need amending. Topsoil (basic): native soil with screening; often compacted, needs amending heavily for vegetable beds. For new raised beds, spend on raised bed mix or build your own from topsoil + compost + aeration.

Should the bed be full to the top? +

Yes — fill to within 1" of the top. Soil settles 10-20% in the first season (from rain compacting, decomposition of organic matter). Mound it at fill time and top up next spring with compost.

How often should I add compost? +

1-2 inches of compost on top of established beds each spring. Compost feeds the soil microbiome, replaces nutrients used by last season's plants, and replaces settled volume. Mix into the top 4-6 inches with a hand cultivator, or sheet-mulch on top and let worms incorporate.

Can I use native soil? +

For most rural sites with reasonable topsoil: yes, mix with compost (30-50%) and aeration. For urban or compacted clay sites: skip native soil and build raised beds with imported mix — too much time/cost to amend clay enough to grow well.

What about pH? +

Most vegetables want pH 6.0-7.0. Most commercial raised bed mixes land in this range. Compost adjusts pH slightly toward neutral. Test pH with a $10 soil test kit if your plants struggle; amend with lime (raise pH) or sulfur (lower pH) as needed.

Hugelkultur — worth doing? +

For deep beds (18"+ depth): yes. Bottom layer of rotting wood logs + sticks + branches, covered with brown organic matter, then soil on top. The wood decomposes over 5-10 years, creating sponge-like water retention and slow nutrient release. Significant savings on bulk soil costs for deep raised beds.

How much does soil weigh? +

Garden soil: 75-100 lb per cubic foot when moist. A 1.5 cu ft bag weighs ~120-150 lb. A cubic yard weighs 1,800-2,500 lb depending on moisture and composition. A pickup truck bed holds about 1-1.5 yards of soil (don't overload your suspension).

What if I'm filling around an existing tree? +

Don't change soil grade around mature trees — more than 4" of soil added near the trunk can suffocate roots and slowly kill the tree. For raised beds near established trees, build outward of the dripline or use a planter that doesn't touch the trunk.