Land Development & Construction

Which Tool for Which Job

Eleven calculators sit under this category, and they sort into four jobs. Get the job straight first, because the tool that answers “how much building can I put here” has nothing to do with the one that answers “is this slope safe to pour a driveway on.”

Feasibility, before you draw. Four numbers decide whether a parcel pencils, and each is a separate cap. The FAR / FSI calculator turns lot area times the permitted ratio into buildable floor area. The building coverage ratio calculator checks how much of the lot the footprint can cover, which stops projects at the permit counter more often than FAR does. The zoning density calculator answers the units-per-acre question, how many dwellings the zone allows, a different limit again. And the plot division planner takes a parent parcel down to a sellable lot count after roads and setbacks come off the top. Run these before you pay for drawings, since any one can kill a concept on its own.

Earthwork, once the site is real. Moving dirt is where budgets swing. Start with the slope and grade calculator to convert a grade between percent, degrees, and rise over run, and to confirm the ground falls away from the house. When you need volumes, the cut-and-fill mass balance tool nets excavation against fill zone by zone and tells you whether to haul dirt in or out, while the fill volume calculator sizes the import when you’re only raising grade, in cubic yards and truckloads. If the grade change needs holding, the retaining wall volume and cost estimator takes off block, backfill gravel, and a rough cost.

The pieces that sit on top. Two tools price the site items rather than the earth under them. The driveway construction cost estimator breaks a driveway or short private road into its layer stack, excavation, base, and surface, and prices each. The fence post spacing and material estimator turns a run length into a post count and a full material list once you know the perimeter.

Safety, kept separate on purpose. The safe gradient checker is the one page here where a wrong number is a hazard, not a budget miss. It compares a slope against the ADA ramp limit and against rule-of-thumb ranges for driveways, walkways, mowing, and unretained cuts. Use the grade calculator to get the number. Use this one to judge whether that number is safe for what you’re building.

How These Tools Compute (Methodology)

None of these is a black box. Slope conversions are trigonometry: percent grade is rise divided by run times 100, and the angle is arctan(rise ÷ run), which is why a 100 percent grade is 45 degrees and not 100. Earthwork volume uses the average-end-area method, averaging the cut or fill depth across a zone and multiplying by area, then adjusting for how soil changes state. Dug soil swells (a bulking factor near 1.25 for average material) and placed fill compacts back down, so the same dirt reads as three different volumes: bank, loose, and compacted. Compaction targets reference ASTM D698, the Standard Proctor test.

The zoning math is deliberately plain. FAR, coverage, and density are each a ratio, floor area or unit count over the lot, so the calculators run exact arithmetic on the values you enter. What they can’t know is your jurisdiction’s definitions, which is the part that actually varies. The safety thresholds are sourced, not invented. The 1 : 12 (8.33 percent) ramp maximum comes from the US Access Board 2010 ADA Standards; the 2 : 1 limit on unretained cuts and the angle-of-repose ranges come from standard geotechnical references; and the driveway grade cap and the retaining-wall height that triggers a permit are set locally, usually off the International Building Code as your building department adopts it. Every computed value is exact on your inputs, but real-world accuracy rides on the survey behind those inputs, which is why the earthwork and wall pages send you to a licensed engineer before anything gets built.

Terms That Trip People Up

FAR / FSI

Floor Area Ratio (Floor Space Index in South Asia). Total buildable floor area across all storeys divided by lot area. A FAR of 2.0 on a 10,000 sq ft lot allows 20,000 sq ft of building.

Lot coverage

The share of the lot sitting under a roof, footprint only. Not the same as FAR: a two-storey and a ten-storey building on the same footprint have identical coverage.

Mass balance

Whether the cut volume on a site covers the fill it needs. A balanced site avoids paying to import or export dirt, often the largest earthwork line item.

Compaction (shrinkage) factor

How much loose fill shrinks once compacted, usually 10 to 25 percent. Order loose yards above your compacted target or the pad comes up short.

Safe gradient

The slope a given surface tolerates, and it’s surface-specific. A driveway, a wheelchair ramp, and a mowed bank each top out at a different grade.

ADA 1 : 12

The maximum running slope for an accessible ramp, one inch of rise per twelve of run, which is 8.33 percent. Landings, handrails, and cross slope are separate requirements on top of it.