Potting Soil Calculator

Use the cylinder formula: V = π × r² × h, where r = radius (half the diameter) and h = height, all in inches. Divide the result by 1,728 to convert cubic inches to cubic feet. This gives you the volume of soil needed.

Common bag sizes: 0.5 cu ft, 1 cu ft, 2 cu ft, and 3 cu ft. Calculate total cubic feet needed, then divide by bag size. Always buy 10—15% extra to account for soil settling and filling gaps around roots.

Leave 1—2 inches of space from the top for watering. Soil settles over time and compact organic matter shrinks. Fill pots to about 90% capacity to prevent overflow when watering and allow room for adding compost top-dressings.

Potting soil (potting mix) is a sterile, lightweight blend designed for containers. It contains perlite, vermiculite, and peat moss for drainage and aeration. Garden soil is denser, may contain pathogens, and compacts in pots, causing drainage problems.

Replace potting soil every 1—2 years for most plants. Soil breaks down, compacts, and loses nutrients over time. Refresh by removing the top 2—3 inches and adding fresh mix, or completely repot plants with new soil annually.

Yes, with precautions. Sterilize old soil by baking at 180°F for 30 minutes or letting it freeze for a week. Mix with 25—50% fresh potting soil to restore structure and nutrients. Remove old roots and debris before reuse.

Dry potting soil weighs approximately 4—8 lbs per cubic foot depending on composition. Peat-based mixes are lighter (4—5 lbs). Soil with more compost or vermiculite is heavier (6—8 lbs). This matters for hanging baskets and elevated planters.

Modern practice recommends against drainage material (rocks, gravel) at pot bottoms. It raises the perched water table, keeping roots wetter. Use pots with drainage holes and quality potting mix instead. A coffee filter over the hole prevents soil loss.

Use a sterile, all-purpose potting mix for most indoor plants. For succulents, use a fast-draining cactus mix. For African violets, use a peat-based mix. Avoid garden soil indoors — it compacts, drains poorly, and may contain pests or diseases.

A 5-gallon bucket holds approximately 0.8 cubic feet of potting soil. One 2-cu ft bag fills about 2.5 buckets. For multiple buckets, calculate: Number of buckets × 0.8 = total cubic feet needed, then add 10% for settling.

Yes. Basic recipe: 1/3 peat moss or coco coir (moisture retention), 1/3 perlite or vermiculite (drainage and aeration), and 1/3 compost (nutrients). For acidic plants, add extra peat. For succulents, increase perlite to 50%. Sterilize components to prevent disease.

Most hanging baskets are 12—16 inches in diameter and 6—8 inches deep. Use the round pot formula: π × r² × h ÷ 1728. A 14-inch basket needs approximately 0.5—0.7 cu ft of soil. Lightweight mixes are essential to prevent basket sagging.

The terms are often used interchangeably, but potting mix technically contains no soil. It's a soilless blend of peat, perlite, vermiculite, and other amendments. Potting soil may contain actual soil. For container gardening, potting mix is preferred for better drainage and aeration.

Window boxes are typically rectangular. Measure length × width × depth in inches. Divide by 1,728 for cubic feet. A standard 24-inch window box needs approximately 0.5—1 cu ft. Don't overfill — leave 1 inch below the rim for watering.

Most commercial potting mixes contain starter fertilizer lasting 3—6 months. For longer growing seasons, add slow-release fertilizer pellets at planting. Liquid fertilizer every 2—4 weeks during active growth provides consistent nutrition. Avoid over-fertilizing, which causes salt buildup.

Expect 10—20% settling in the first few months as organic matter decomposes and air pockets collapse. Fill pots 1—2 inches below the rim initially. Top off with fresh mix or compost as needed. Completely replace soil every 1—2 years for optimal plant health.

Yes, but it's expensive for large areas. Potting soil works well for raised beds, container gardens, and transplanting. For in-ground planting, amend native soil with compost instead. For raised beds, mix 50% potting soil with 50% topsoil for a cost-effective blend.

For 1—2 small pots, a 1-cu ft bag suffices. For 3—5 medium pots, buy 2 cu ft. For large containers or many pots, 3-cu ft bags or bulk delivery (by the cubic yard) is more economical. Calculate total volume first, then choose the most cost-effective packaging.

Poor potting soil: excessive dust, compacted texture, poor drainage, strong chemical smell, visible fungus gnats, or hydrophobic (water-repellent) surface. Good potting soil: light, fluffy texture, drains well, smells earthy, and absorbs water quickly when dry.

Store in a cool, dry place in the original bag or sealed container. Keep it slightly moist (not wet) to prevent peat from becoming hydrophobic. Use within 6 months to 1 year. Old potting soil loses nutrients and structure but can be refreshed with compost.

Organic potting soil uses natural ingredients without synthetic fertilizers or pesticides. It's worth it for edible gardens, sensitive plants, and environmentally conscious gardeners. For ornamentals, conventional potting soil works fine. Organic mixes may cost 20—50% more but provide safer growing media.

The Potting Soil Calculator uses exact, globally standardized conversion constants from authoritative sources like NIST (National Institute of Standards and Technology).

Results are displayed with sufficient decimal places for practical use. For most applications, the precision exceeds what is needed for everyday calculations.

Yes, most converters include a swap button that instantly reverses the "from" and "to" units, allowing you to convert in either direction.