How to use the lot coverage calculator
- Choose square feet or square meters, then enter the lot area, or switch to width and depth and let the page multiply them.
- List each structure with the area of its footprint, which is the ground area under its roof. Add rows for a garage, shed or addition.
- To compare with a limit, enter the coverage limit from your own rules. No limit is built in.
- Read the lot coverage, the open ground and, with a limit, the footprint still available or the amount over, shown in parentheses.
Formula
lot coverage = total footprint / lot area x 100
footprint allowed = lot area x limit / 100
footprint available = allowed - total footprint
The result is shown to two decimals. If the footprints add up to more than the lot, the page warns you, since that usually means a typing mistake or a mismatch of units.
A house, garage and shed on a 7,500 square foot lot
A house with an 1,800 square foot footprint, a 480 square foot garage and a 96 square foot shed cover 1,800 + 480 + 96 = 2,376 square feet. On a lot of 7,500 square feet that is 2,376 / 7,500 x 100 = 31.68% coverage, leaving 5,124 square feet of open ground.
With a limit of 35% the lot allows 7,500 x 35 / 100 = 2,625 square feet of footprint, so 249 square feet are still available. With a limit of 25% the allowance is 1,875 square feet, and the plan is over by (501 square feet). A lot entered as 75 by 100 feet gives the same 7,500.
What lot coverage measures
Lot coverage compares the ground taken by buildings with the size of the lot. It differs from floor area, which adds every level of a building. A two story house with a 1,200 square foot footprint covers the same ground as a one story house of 1,200 square feet, even though it has twice the floor area. The Floor Area Ratio Calculator covers the second measure.
Rules about coverage are usually local, and they differ on what counts. Some include porches, decks, carports and overhangs, and some exclude them. Some set a separate limit for paved surfaces. This calculator adds only the areas you enter, so measure what your own rules count and enter that.
Measuring a footprint
Measure the outside of the walls, or the roof edge if your rules use it, and multiply length by width. For an L shape, split it into two rectangles and enter each as its own row. The Square Footage Calculator and the Area Calculator help with the arithmetic. Use the same unit for the lot and the buildings.
If you plan an addition, add a row for it and see how much room is left. The percentage updates as you type, which makes it easy to try a smaller garage or a different shed. For cost planning once the size is set, the Renovation Budget Planner is the next step.
Assumptions and limits
- The lot and every footprint use the same unit, chosen at the top.
- Footprints are added as entered. Overlapping areas, such as a deck attached to a house, are counted twice if you list both.
- A limit, if you enter one, comes from your own rules. The tool contains no legal limits and gives no advice about permits.
- Nothing is stored or uploaded.
Frequently asked questions
How do I calculate lot coverage?
Add the footprint areas of all buildings and divide by the lot area, then multiply by 100. With 2,376 square feet of buildings on a 7,500 square foot lot, the coverage is 31.68%.
Does lot coverage include the driveway?
It depends on the rules that apply to you. Some count only roofed buildings, and some also count paved areas. Enter whichever areas your rules count, and leave out the ones they do not.
What is the difference between lot coverage and floor area ratio?
Lot coverage uses the ground footprint of buildings, while floor area ratio uses the floor area of all levels. A tall building can have low coverage and a high floor area ratio.
What if my coverage is over the limit?
The page shows how far over you are in parentheses, in the same unit as the lot. To bring it down, reduce a footprint, drop a structure, or check whether your rules allow an exception. Ask the office that sets the rules for the exact requirement.