Lawn & Garden · 8 calculators
Lawn & Garden questions, answered
Order mulch, topsoil, gravel, sand, seed and sod, and plan fertilizer and watering for a yard. 8 questions, one per calculator, each naming its formula and figure at documented inputs. Open any one to swap in your own numbers. Every answer in Lawn & Garden states the calculator’s formula, the worked-example inputs behind the figure, the result at those inputs and the point where the model stops being a reasonable approximation, so each number can be checked against your own situation before you rely on it. The questions in Lawn & Garden run from the ones most people ask first to the ones that only matter once the basics are settled, and every answer links to the calculator that produced its figure, so the reasoning and the arithmetic can be read side by side and challenged separately.
Common lawn & garden questions
How deep should mulch be?
About 2 to 3 inches for most beds. Under 2 inches lets weeds through, and over 4 inches can smother roots and hold too much moisture. Keep it a few inches back from trunks and stems.
How many square feet does a cubic yard cover?
A cubic yard covers 324 square feet at 1 inch deep, 162 at 2 inches, 108 at 3 inches and 81 at 4 inches. The calculator does this for any area and depth.
Is it cheaper to buy in bulk or in bags?
Usually bulk once you pass about a cubic yard, which is 13 or 14 two-cubic-foot bags. Bags cost more per yard but are easier to carry and store, and bulk needs a delivery spot.
Do bulk materials settle after delivery?
Yes. Soil and mulch settle by 10 to 20 percent and stone compacts by about 10 to 15 percent, so round the order up rather than down.
Why is the tonnage different from what I expected?
Weight per cubic yard depends on the material and its moisture. Gravel is about 1.3 to 1.6 tons, sand about 1.3 to 1.4 and topsoil about 1.1, and rain adds to all of them.
How much water does a lawn need?
About 1 inch a week, counting rain, is a common target for cool-season grass. Water deeply two or three times a week rather than a little every day, so roots grow down.
How do I read the numbers on a fertilizer bag?
They are the percent nitrogen, phosphorus and potassium by weight. A 20-5-10 bag is 20 percent nitrogen, so 15 pounds of it holds 3 pounds of nitrogen.
When is the best time to seed a lawn?
Early fall for cool-season grasses, when soil is warm and air is cool, and late spring for warm-season grasses. Both need about 2 to 3 weeks of even moisture to sprout.
Do these calculators handle sloped or curved beds?
They use a flat area you enter. For a curve, split the bed into rectangles and circles, add their areas, and add 5 to 10 percent for the awkward edges.
Lawn & Garden at a glance: each result, and the input that moves it most
| Calculator | Result at the worked example | Input that moves it most |
|---|---|---|
| Mulch Calculator | Mulch needed (cubic yards): 3.7 | Bed area (sq ft) (0.741 (20%)) |
| Topsoil Calculator | Topsoil needed (cubic yards): 6.2 | Soil depth (in) (1.2 (20%)) |
| Gravel Calculator | Gravel needed (cubic yards): 5.6 | Area to cover (sq ft) (1.1 (20%)) |
| Sand Calculator | Sand needed (cubic yards): 1.2 | Sand depth (in) (0.247 (20%)) |
| Grass Seed Calculator | Seed needed (lb): 30 | Seeding rate (5 (67%)) |
| Lawn Fertilizer Calculator | Fertilizer needed (lb): 25 | Nitrogen in the bag (%) (5.1 (20%)) |
| Sod Calculator | Rolls needed: 126 | Area to cover (sq ft) (25 (20%)) |
| Lawn Watering Calculator | Water per week (gallons): 1,869 | Lawn area (sq ft) (373.8 (20%)) |
How to calculate each lawn & garden figure
How do I calculate mulch?
Cubic yards = area × depth (in) ÷ 12 ÷ 27; bags = cubic feet ÷ bag size. Order the right amount of mulch for a garden bed or around a tree in one trip. The prefilled example returns a mulch needed (cubic yards) of 3.7.
How do I calculate topsoil?
Cubic yards = area × depth (in) ÷ 12 ÷ 27; bags = cubic feet ÷ bag size; tons = cubic yards × weight per cubic yard. Decide between bulk delivery and bags, and order the right weight for a truck. Using the worked example on the page, the topsoil needed (cubic yards) works out to 6.2.
How do I calculate gravel?
Cubic yards = area × depth (in) ÷ 12 ÷ 27; tons = cubic yards × weight per cubic yard. Order stone by the ton for a surface of a given area and depth. At the worked-example inputs the gravel needed (cubic yards) is 5.6.
How do I calculate sand?
Cubic yards = area × depth (in) ÷ 12 ÷ 27; tons = cubic yards × weight per cubic yard. Order a sand base or a sandbox fill without guessing the volume. Using the worked example on the page, the sand needed (cubic yards) works out to 1.2.
How do I calculate grass seed?
Seed (lb) = area ÷ 1,000 × seeding rate (lb per 1,000 sq ft); bags = pounds ÷ bag size. Buy the right amount of seed for a new lawn or an overseeding job. Using the worked example on the page, the seed needed (lb) works out to 30.
How do I calculate lawn fertilizer?
Product (lb) = area ÷ 1,000 × nitrogen rate ÷ (nitrogen % ÷ 100); bags = pounds ÷ bag weight. Apply the labeled amount of nitrogen and no more, whatever the bag's strength. At the worked-example inputs the fertilizer needed (lb) is 25.
How do I calculate sod?
Rolls = ⌈area × (1 + waste) ÷ roll area⌉. Order enough sod to finish the job in one delivery, because it must be laid fresh. Using the worked example on the page, the rolls needed works out to 126.
How do I calculate lawn watering?
Gallons = area × inches of water × 0.623; minutes = gallons ÷ sprinkler flow (gallons per minute). Turn an inch of water a week into the minutes to run a sprinkler. Using the worked example on the page, the water per week (gallons) works out to 1,869.
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