Building Coverage Ratio Calculator

Net Site Area = Gross Site Area − Non‑Buildable/Excluded Area

Total Coverage Area = Main Footprint + (Selected covered components) + (Optional overhang addition)

Building Coverage Ratio (%) = (Total Coverage Area ÷ Net Site Area) × 100

1. Pick one unit and use it everywhere.
2. Enter gross site area and any excluded/non-buildable area.
3. Enter the main building footprint (ground coverage).
4. Optionally add accessory, patio, and carport areas, then tick “Include”.
5. Only enable overhang addition if your local rule counts it.
6. Enter a maximum allowed ratio to check compliance and remaining area.
7. Click Calculate, then download CSV or PDF for records.

Building coverage ratio in construction

Building Coverage Ratio (BCR) is a quick way to understand how much of a site is occupied by covered structures at ground level. Planners, architects, and contractors use it to confirm a layout fits zoning or covenant limits before detailed design begins. Unlike floor area ratio, BCR focuses on the footprint that reduces open space and can affect access, drainage patterns, and fire separation.

A professional check starts by defining the net site area. Many plots include exclusions such as public right‑of‑way dedication, easements, environmental buffers, steep-slope protection, or utility corridors. Subtract these from gross site area to avoid a misleadingly low ratio. Next, add the covered components your jurisdiction counts. Some rules include accessory sheds, covered porches, and carports; others exclude them. This calculator lets you toggle each item so your report matches the local interpretation.

BCR supports early trade-offs. If the ratio is high, you may reduce the footprint, move parking to uncovered stalls, consolidate accessory spaces, or adjust setbacks to improve usable outdoor area. When a maximum limit is provided, the calculator also shows the allowable coverage area and the remaining capacity. A positive remaining value means you can still add covered area; a negative value indicates the design exceeds the limit.

Worked example

Suppose a residential plot has gross site area 500 m² with 50 m² excluded for easements. Net site area becomes 450 m². The main footprint is 220 m², and an accessory room adds 30 m² (included). Total coverage area is 250 m². The BCR is (250 ÷ 450) × 100 = 55.56%. If the allowed limit is 60%, allowable coverage is 270 m², leaving 20 m² capacity.

For project documentation, keep your inputs consistent and record the source of exclusions (survey, title notes, or authority guidance). If your local rules treat roof overhangs differently, use the optional overhang addition only when required and document the assumption in Notes. During permitting, reviewers commonly look for clear math and traceable areas; exporting the CSV or PDF helps preserve a transparent calculation trail for coordination between design, estimating, and field teams.

FAQs

1) What does building coverage ratio measure?

It measures the percentage of the net site area covered by building footprints and selected covered features at ground level. It is used to check open-space and zoning compliance.

2) What is the difference between gross and net site area?

Gross site area is the total plot area. Net site area removes excluded or non-buildable portions such as easements, protected zones, or dedicated right-of-way, depending on local definitions.

3) Should carports and covered patios be included?

Rules vary. Some authorities count any roofed structure; others exclude certain features. Use the Include checkboxes to match your jurisdiction, and note the basis in your documentation.

4) Does the calculator handle multiple buildings?

Yes. Treat the main footprint as the primary structure and add accessory footprints as needed. For several separate buildings, sum their footprints into the relevant input fields.

5) Why is my coverage ratio above 100%?

That typically means total included coverage area is larger than net site area. Recheck units, excluded area, and included components. It can also indicate an input mistake or mismatch in area definitions.

6) What does “remaining allowable area” mean?

It equals allowable coverage area minus your total coverage area. Positive values show remaining capacity under the limit. Negative values show the amount of overage that must be reduced.

7) How should I use overhang addition?

Only enable it if your local standard counts eaves or canopies toward coverage. Enter a percentage of the main footprint and keep an approval note stating the rule you followed.