Mulch, Soil & Gravel: A Practical Buying Guide

The Key Conversion: Cubic Yards vs. Cubic Feet

All bulk landscaping materials are sold by the cubic yard. Bags at the hardware store are labeled in cubic feet. Knowing how to convert between them is the entire math of this category:

A 2 cu ft bag of mulch is a common bag size. One cubic yard of bulk mulch equals 13.5 bags (27 ÷ 2 = 13.5). If bulk mulch costs $40/cu yd and bags cost $5 each, the bulk price is $40 while the bag equivalent is $67.50. Bulk is nearly always cheaper at scale — but only if you can use the full amount and have the labor and equipment to spread it.

How to Measure Your Beds

All landscape material calculations need two measurements: the areaof the bed (in square feet) and the desired depth (in inches). Area × depth ÷ 12 (to convert inches to feet) gives you volume in cubic feet, which you then divide by 27 for cubic yards.

Rectangular Beds

Length × Width = square feet. Straightforward.

Irregular Beds

For curved or irregular beds, break them into approximate rectangles or use the following shortcut: measure the longest length and widest width, calculate as a rectangle, then multiply by 0.8 (accounting for the area lost at the edges of a curved bed). For very irregular shapes, divide the bed into sections and calculate each separately.

Total Formula

The 324 factor is 27 × 12, combining the cu yd to cu ft conversion and the inch to foot conversion in one step. If you prefer to work step by step:

1. Area in sq ft × depth in inches = total in sq ft·inches
2. Divide by 12 → cubic feet
3. Divide by 27 → cubic yards

Example: A bed that is 20 × 8 ft, to be mulched 3 inches deep: (20 × 8 × 3) ÷ 324 = 480 ÷ 324 = 1.48 cubic yards.

The Mulch Calculator handles this instantly for any bed size and depth.

Recommended Depths by Material and Use

Mulch depth note:More than 4 inches of mulch can cause moisture retention problems and root suffocation, especially around tree trunks. Keep mulch 2–3 inches away from any tree trunk or plant stem (the “mulch volcano” mistake that kills more trees than almost any other landscaping error).

Choosing the Right Material

Mulch Types

• Hardwood bark mulch: Most common. Breaks down over 1–2 seasons, adding organic matter to the soil. Good for flower beds and foundation plantings.
• Pine bark nuggets: Slower to break down. Tends to float in heavy rain. Better for well-drained areas without significant runoff.
• Cedar or cypress mulch: Natural insect-repelling oils. Longer lifespan than hardwood. More expensive, but popular around home foundations.
• Straw or hay: Best for vegetable gardens and new-seeded lawns. Not appropriate around foundation plantings (attracts rodents).
• Rubber mulch: Longest lifespan (10–20 years). Does not break down to improve soil. Primarily used in playgrounds and commercial settings.

Topsoil vs. Compost vs. Fill Dirt

• Topsoil: The upper layer of existing soil, sold as a product. Quality varies significantly by source. Good topsoil is dark, crumbly, and free of rocks and weed seeds. Use for new garden beds, raised lawn areas, and top-dressing.
• Compost: Decomposed organic matter with high nutrient content. Better as an amendment (mixed into existing soil) than as a standalone growing medium for most applications. Usually sold in bags at hardware stores or in bulk from composting facilities.
• Fill dirt: Subsoil (below the topsoil layer) used for grading, leveling, and filling low spots. No organic matter, not suitable for growing plants. Much cheaper than topsoil. Use to correct drainage or grade before adding topsoil.
• Garden mix: A blend of topsoil, compost, and sometimes perlite or sand. Best for raised garden beds. More expensive than topsoil alone, but provides the drainage and nutrients vegetables need.

Gravel and Stone Types

• Pea gravel: Rounded, smooth, 3/8-inch stone. Best for drainage beds, between pavers, and under trampolines. Shifts underfoot and is not ideal for high-traffic pathways.
• Crushed stone (#57 or #411): Angular crushed limestone or granite. Compacts well. Best for driveway bases, pathway bases, and drainage applications.
• River rock: Smooth, decorative stone in larger sizes (1–3 inch). Used as decorative ground cover. Does not compact and is not suitable as a base layer.
• Decomposed granite: Fines down to a powder-like texture that packs hard. Popular for pathways, patios, and Southwestern-style landscapes.

Bulk vs. Bagged: The Cost Comparison

The breakeven point where bulk becomes cheaper than bags depends on your area, but the general pattern holds almost everywhere:

• Under 1 cubic yard: Bags are more convenient. The delivery minimum for bulk often makes it more expensive for small orders.
• 1–3 cubic yards: Compare bulk delivered price to bag equivalent. In most markets, bulk wins by 20–40%.
• Over 3 cubic yards: Bulk is almost always significantly cheaper, and easier to unload with a wheelbarrow than carrying dozens of bags.

Important: bulk delivery charges vary. Some suppliers charge flat delivery fees; others charge by distance. Always ask for the total delivered price, not just the per-yard rate.

Estimating for Multiple Beds

If you have multiple beds, calculate each separately and add the totals. Round up to the nearest cubic yard for bulk orders. For bag purchases, round up to the nearest whole bag.

Example: Three flower beds: 120 sq ft, 85 sq ft, and 60 sq ft, all at 3 inches depth.

• Total area: 120 + 85 + 60 = 265 sq ft
• Cubic yards: (265 × 3) ÷ 324 = 2.45 cu yd
• Add 10% for settling and edges: 2.45 × 1.10 = 2.70 cu yd → Order 3 cu yd

The Mulch Calculator, Soil Calculator, and Gravel Calculator all give you cubic yards, cubic feet, and bag counts in one calculation.