Calculator
Formula used
The ground coverage ratio expresses how much of a plot is covered at ground level. It is commonly evaluated as a percentage.
Your local code may define “coverage” differently. Use the coverage basis option to match your requirement.
How to use this calculator
- Select the area unit used on your drawings.
- Enter plot area, or provide plot length and width.
- Enter main footprint area, or provide its length and width.
- Add any extra covered structures such as garages or sheds.
- Optionally add extra impervious area and a maximum limit.
- Press Calculate to view results above this form.
Example data table
| Scenario | Plot Area (m²) | Building Footprint (m²) | Extra Impervious (m²) | Coverage Basis | GCR (%) |
|---|---|---|---|---|---|
| Residential lot | 500 | 180 | 40 | Building footprint only | 36.00 |
| Residential with hardscape | 500 | 180 | 40 | Building + additional impervious | 44.00 |
| Small commercial | 1200 | 520 | 130 | Building + additional impervious | 54.17 |
Use these examples to sanity‑check your own inputs.
Why ground coverage ratio matters
Ground coverage ratio (GCR) shows how much land is occupied at ground level by buildings and hard surfaces. Reviewers use it to protect drainage, access, daylight, and neighborhood character. Lower GCR leaves more permeable area for infiltration and landscaping. On compact plots, small footprint changes can shift GCR enough to trigger redesign. This calculator lets you test options before drawings are issued.
Choosing the right coverage basis
Rules define “coverage” differently. Some count only roofed footprint; others include driveways, patios, and slabs as impervious coverage. The basis selector helps you match the calculation to the applicable standard and record the assumption. If you are unsure, run both bases and compare results. The difference shows how much hardscape contributes, guiding choices like permeable paving or reduced apron widths.
Common input sources and checks
Inputs usually come from surveys, site plans, and CAD takeoffs. Use plot dimensions from boundary data, and footprint areas from architectural plans. Add secondary structures such as garages, kiosks, canopies, and service rooms as separate rows so totals remain auditable. Keep units consistent and avoid mixing rounded areas with precise dimensions. If coverage exceeds plot area, treat it as a data issue, not a design outcome.
Interpreting limits and margins
Entering a maximum percentage adds an allowed coverage area and a margin. Positive margin means capacity for additions; negative margin indicates noncompliance. During iterations, track margin because it converts directly into usable area. Near the limit, adjust footprint geometry, revise parking layout, or reduce nonessential hardscape to recover margin. Pair the result with setback and height checks to avoid single-metric decisions.
Reporting and record keeping
For submissions, note the basis, unit system, and the component breakdown used. CSV export supports spreadsheets and cost models, while PDF output provides a clean appendix for permit packages. Save results by revision date and rerun after plan updates, scope changes, or survey revisions. Clear, repeatable records reduce review questions and shorten approval cycles and client coordination.
FAQs
What is ground coverage ratio?
Ground coverage ratio is the coverage area divided by the plot area, expressed as a percentage. Coverage can be building footprint only or footprint plus other impervious surfaces, depending on local rules.
Which areas should be included in building footprint?
Include all roofed areas measured at ground level, such as the main building, attached garages, covered porches, canopies, and permanent overhangs if your authority counts them. Exclude upper floors unless they project at grade.
When should I include driveways and patios?
Include them when your code defines coverage as impervious area or site coverage. If rules are unclear, calculate both bases and consult the zoning note or reviewer to confirm the correct interpretation.
Can I use length and width instead of area?
Yes. Enter plot length and width to auto-calculate plot area, and enter building length and width to auto-calculate footprint area. If both area and dimensions are provided, dimensions take priority.
What does a negative margin mean?
A negative margin means the proposed coverage area exceeds the allowed coverage computed from your limit percentage. Reduce footprint, remove hardscape, or increase effective permeable area to return within the limit.
How accurate are the CSV and PDF downloads?
Downloads reflect the most recent calculation stored in your session. They are suitable for internal documentation and permit appendices, but you should still verify inputs against stamped drawings and jurisdiction-specific definitions.