How we calculate

Arithmetic is never done by AI

This is the rule the whole site is built around. Every quantity, cubic yards, bag counts, pounds of seed, run times, cost ranges, is computed by deterministic code from documented formulas. A language model never produces, adjusts, or rounds any number you see.

The assistant panels on some calculators do use AI, and they only ever receive results that were already computed. Their job is interpretation and sequencing: what the number means for your weekend, what order to do things in, what usually goes wrong. If you turn the assistant off, or the API key is missing, every calculation still works exactly the same.

Exact conversions

These are definitions, not approximations, and we carry them at full precision through every intermediate step:

• 1 foot = 12 inches; 1 yard = 3 feet
• 1 cubic yard = 27 cubic feet
• 1 square yard = 9 square feet
• 1 acre = 43,560 square feet
• 1 inch = 2.54 centimetres (exact by definition)
• 1 US gallon = 231 cubic inches
• 1 pound = 0.45359237 kilograms (exact by definition)
• 1 US ton = 2,000 pounds

One inch of water over one square foot is 144 cubic inches, or 0.6234 US gallons. That is where the 623 gallons per 1,000 square feet per inch figure in the irrigation calculators comes from.

The irrigation constant 96.25, used to turn gallons per minute into inches per hour, is 60 × 231 ÷ 144. It is exact.

Where we round

Nothing is rounded during a calculation, only at the point of display. That avoids the compounding error you get when each step is rounded before feeding the next.

Purchasable units, bags, pallets, pavers, posts, always round up, because you cannot buy nine tenths of a bag. We do guard against floating-point noise: a computed 4.0000001 bags is treated as 4, not 5.

Densities are typical, and editable

Loose bulk materials have no single correct density. Weight per cubic yard varies with moisture, screen size, and how long the pile has sat, soaked mulch can weigh half again what dry mulch does. Every density we publish is a typical mid-range figure, shown alongside its realistic spread, and every calculator that uses one lets you override it.

This matters less than it sounds, because volume never depends on density. Area × depth decides how much you buy. Density only converts that volume into a delivery weight, so an imperfect density affects the “will it fit in my truck” answer and nothing else.

Concrete is the exception: normal-weight concrete is consistently about 150 lb per cubic foot, so 4,050 lb per cubic yard is a reliable figure rather than an estimate. Bag yields (0.30, 0.375, 0.45, and 0.60 cubic feet for 40, 50, 60, and 80 lb bags) are manufacturer specifications and consistent across brands.

Agronomic rates

Seeding rates, nitrogen ranges, and mowing heights reflect the guidance published by US land-grant university extension programs. We present them as ranges because that is how they are published, the right rate genuinely depends on seed purity, soil preparation, and how quickly you need cover.

Where a bag prints its own rate, use that. A specific cultivar blend's label beats any species-level figure, and our calculators let you enter it.

Cost ranges are planning figures, not quotes

Landscape pricing varies more by market than almost any other trade. The same 400 square foot paver patio can differ two-fold between a low-cost interior metro and a coastal one, and contractors price access, slope, and disposal individually.

Our ranges describe the normal span of residential quotes, adjusted by a regional multiplier you select. They are not survey data, and we do not attribute them to sources we have not read. Treat the output as a sanity check on quotes you receive, if three bids land at double the high end, something in the scope differs from what you assumed, and that is worth asking about.

What these calculators cannot tell you

• Whether your base is adequate. We give standard depths by traffic type. Local frost depth, soil bearing capacity, and drainage can all demand more.
• What your local code requires. Permit thresholds, fence heights, setbacks, retaining wall engineering, backflow prevention, and phosphorus restrictions are all local. Check before you build.
• What is buried in your yard. Call 811 before digging. It is free and it is required in most of the US.
• What your specific supplier stocks. Pallet coverage, bag sizes, and bulk pricing vary. Confirm before ordering.

Corrections

If a formula here is wrong, or a figure has drifted out of date, we want to know. We correct pages rather than leaving them to rot, and the update date on every guide and calculator reflects the last substantive change, not a cosmetic edit made to look fresh.

Get in touch if you find something off.