How to use the parking calculator
Parking often decides how much of a site is left for the building. A zoning minimum of four spaces per 1,000 square feet can mean the car park is bigger than the shop it serves, so it pays to size it before massing starts. This calculator answers the three questions that come up first: how many spaces, how many of them accessible, and how much land they need.
- Pick the units you work in, feet or metres.
- Choose a land use. The ratio fills in with a typical planning value. Overwrite it with the number from your zoning code; it is the single most important input.
- Enter the project size: floor area for offices, retail and industrial uses, or the number of dwelling units or hotel rooms for residential uses.
- Set the layout. Pick a stall angle and adjust the stall and aisle sizes if your jurisdiction uses different ones.
- Add an allowance for landscaping islands, walkways and driveways, and optionally enter the area you have for parking to see how many cars fit.
The results show required spaces, accessible and van-accessible spaces from the 2010 ADA Standards, the width of one parking module, the area per car and the total parking area.
Parking formulas
Required spaces = Ratio × (Floor area ÷ 1,000 ft²) or Ratio × Units (round up)
Angled stall depth = Depth × sin(angle) + Width × cos(angle)
Curb length per stall = Width ÷ sin(angle)
Module = 2 × Stall depth + Aisle
Area per car = Module × Curb length ÷ 2 × (1 + Allowance)
A module is one aisle with a row of stalls on each side, which is how surface lots and parking decks are planned. Halving the module area along one stall width gives the area each car takes, before landscaping and access drives.
| Layout | Typical stall | Typical aisle | Module width |
|---|---|---|---|
| 90°, two-way | 9 × 18 ft (2.5 × 5.0 m) | 24 ft (6.0 m) | 60 ft (16.0 m) |
| 60°, one-way | 9 × 18 ft | 18 ft | about 58 ft |
| 45°, one-way | 9 × 18 ft | 13 ft | about 51 ft |
| Total parking spaces | Accessible spaces (ADA Table 208.2) |
|---|---|
| 1–25 | 1 |
| 26–50 | 2 |
| 51–75 | 3 |
| 76–100 | 4 |
| 101–150 | 5 |
| 151–200 | 6 |
| 201–300 | 7 |
| 301–400 | 8 |
| 401–500 | 9 |
| 501–1,000 | 2% of total |
| 1,001 and over | 20, plus 1 per 100 over 1,000 |
Worked examples
A 40,000 ft² office building
At 3 spaces per 1,000 ft², the office needs 40 × 3 = 120 spaces. ADA Table 208.2 puts 101–150 spaces at 5 accessible stalls, and one of those must be van accessible. With 9 × 18 ft stalls on a 24 ft aisle, the module is 60 ft wide and each car takes 60 × 9 ÷ 2 = 270 ft². A 20% allowance brings that to 324 ft², so the lot needs about 120 × 324 = 38,880 ft², or roughly 0.89 acre. That is almost as much land as the building's floor area.
A 90-unit apartment block in metres
At 1.5 spaces per unit, 90 units need 135 spaces, 5 of them accessible and 1 van accessible. With 2.5 × 5.0 m stalls and a 6.0 m aisle, the module is 16 m and each car takes 16 × 2.5 ÷ 2 = 20 m², or 24 m² with the allowance. The parking needs about 135 × 24 = 3,240 m², which is a strong argument for a podium or basement deck on a tight urban site.
Will 60 degree parking fit?
A 15,000 ft² strip of land is set aside for angled parking. At 60° with 9 × 18 ft stalls, each stall reaches 18 × 0.866 + 9 × 0.5 = 20.1 ft from the aisle and takes 9 ÷ 0.866 = 10.4 ft of curb. On an 18 ft aisle the module is about 58.2 ft, so each car takes about 302 ft², or 363 ft² with the allowance. The strip holds about 41 cars, compared with 46 at 90°.
Who this calculator helps
- Architects testing site capacity at feasibility stage, when parking often limits how much building fits.
- Urban designers and planners comparing surface parking with structured or shared parking.
- Developers checking whether a site's numbers work before paying for a full layout.
- Landscape architects planning islands, trees and pedestrian routes through a car park.
- Architecture students learning how stalls, aisles and modules set out a car park.
Tips for planning parking
- Check whether your zoning code sets a minimum, a maximum or both. Many cities have cut or removed parking minimums near transit.
- Lay out the long side of the lot parallel to the modules so you lose fewer stalls at the ends.
- Put accessible stalls on the shortest accessible route to the entrance, and check any level change with the ADA ramp slope calculator.
- Compare the parking area with what zoning allows you to build using the floor area ratio calculator, and measure irregular sites with the square footage calculator.
- For decks and podiums, add space for ramps, columns and stair cores; structured parking usually needs about the same area per car as a surface lot, or more.
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