Formula & constants
Federal ADA 2010 scoping: 1 accessible space for 1–25 total, 2 for 26–50, rising to 9 for 401–500, then 2% up to 1,000 and 20 plus 1 per 100 beyond. At least 1 in every 6 accessible spaces must be van-accessible. Critically, the count is calculated per parking facility, not per site — three lots totalling 900 spaces need more accessible stalls than one 900-space lot. All default values are editable — when your supplier's data sheet or local code says otherwise, use that number.
Where this fits in your project
This tool is one step in a bigger job. Once you have these numbers, parking lot paving calculator (Parking Lot Paving Calculator), then asphalt calculator (Asphalt Calculator). For the full sequence see the project workflows, compare approaches on the comparison pages, and check local factors in the state guides.
Frequently asked questions
How many ADA parking spaces do I need?
It scales with the total in each facility: 1 space for lots of 1–25, 2 for 26–50, 3 for 51–75, 4 for 76–100, up to 9 for 401–500. Lots of 501–1,000 need 2% of the total, and above 1,000 the formula is 20 plus 1 for each additional 100 spaces.
Do I calculate ADA spaces per lot or for the whole site?
Per parking facility. This is the single most common and most expensive compliance error — a site with three separate lots is scoped three times, which usually yields more required accessible spaces than treating it as one combined total.
How many van-accessible spaces are required?
One in every six accessible spaces, or fraction of six, under federal ADA. Massachusetts requires one in eight. In California, outpatient medical facilities must make every accessible space van-accessible.
Does California differ from federal ADA?
Yes, and expensively. California Building Code Chapter 11B requires 98-inch vertical clearance at every accessible space, not just van spaces — a retrofit that can cost $50,000 to $200,000 in a structured garage if caught late.
Do employee-only lots need accessible parking?
Yes. The 2010 Standards apply to employee parking with the same scoping table as visitor lots.
Last verified: — See our methodology.
Planning estimates only — confirm quantities with suppliers and local code before ordering.