Every listing quotes gross acreage. None of your buyers will pay for it. Between the survey and the plat, a meaningful share of the site disappears into roads, detention, open space and land you simply cannot build on — and the order you take those deductions in changes the answer.
Start with what the jurisdiction takes
Right-of-way and internal streets come first, because they are the least negotiable. On a typical single-family subdivision they run between 15 and 22 percent of gross. Detention and drainage follow; in flat, wet markets that number climbs fast.
- Roads and right-of-way: 15–22% of gross
- Detention and drainage: 5–10%
- Open space and amenity: 3–8%
- Wetlands, floodway and slope: site-specific — measure, do not guess
Then divide by the lot you can actually sell
Divide net developable area by the lot your builder will buy, not the minimum the zoning allows. A 50-foot product on a 60-foot buyer’s market leaves you with lots nobody wants at the price your pro forma assumed.
The lot count is the first number every other number depends on. Get it wrong and the margin is fiction.
Pencl’s Lot Estimator runs these deductions in the same order every time and draws a concept site plan to match, so the count you underwrite is one you can defend.
