Sri Lanka Floor Area Ratio (FAR) & Plot Coverage Calculator

The Urban Development Authority publishes a Schedule of Planning Standards under the UDA Law No. 41 of 1978 (as amended). For each declared land-use zone the Schedule fixes four hard numbers: the Floor Area Ratio cap, the plot-coverage cap, the maximum number of storeys, and the minimum road-frontage width. Together they bound the legal building envelope on any plot inside the UDA area — which today covers all of Western Province plus the gazetted town and city limits across the island.

1. Normalise the plot extent to m². 1 perch = 25.2929 m²; 1 sq ft = 0.092903 m² (Survey Department of Sri Lanka conversion table).
2. Look up the four zone parameters from the UDA Schedules table: { farMax, coveragePctMax, storeysMax, minFrontageM }.
3. Compute the headline numbers: maxFootprint = plotArea × coveragePctMax and maxFloorArea = plotArea × farMax.
4. Apply the corner-plot uplift where it applies: +5 percentage points on coverage, capped at the 80% absolute ceiling.
5. Determine the binding storey count: maxStoreys = min(storeysMax, floor(maxFloorArea ÷ maxFootprint)). Whichever of the two caps is reached first becomes the constraint on the engineer's design.
6. Run the road-frontage check. If the entered frontage is below the zone minimum, the calculator flags the gap and notes that Special Permission would be required.

Internally the calculator runs the bracket-style storey decision first and also exposes a reconstructByFootprintStoreys helper that recomputes the envelope from maxFootprint × maxStoreys. The two paths reconcile to the m² — when they disagree, the FAR cap is binding and an engineer must reduce the per-floor footprint to unlock additional storeys. The page surfaces this directly in the design-envelope check so you can test a concrete floor plan, not just the headline ceiling.

National defaults vs city plans

The Schedules of Planning Standards are the national defaults. Each gazetted Development Plan — Colombo, Kandy, Galle, Negombo, Matara — can tighten the defaults inside its boundary, and several do. Inside Colombo Municipal Council, for example, large stretches of Cinnamon Gardens carry a Primary Residential designation with a 2-storey cap that the city plan reinforces with heritage-overlay setbacks. Coastal Conservation Department overlays bite inside the 300-m setback line from the high-water mark and can suppress development entirely. v1 of this calculator runs national defaults only; the result is therefore the upper bound on what you may build. Always cross-check the city-plan map and any applicable overlay before purchase or design lock-in.

The five edge cases the calculator handles

Five edge cases are worth flagging. (1) Zero or negative extent collapses to a clean "below minimum" state with no NaN — handy when someone clears the input. (2) Very large extents (above 10,000 perches) trigger a soft warning; the math still runs, but few real plots are that large outside agricultural land outside UDA jurisdiction. (3) Corner plots in zones with coverage ≥ 75% receive a capped uplift, never breaching the absolute 80% ceiling. (4) Sub-frontage plots produce a specific warning quoting the gap (e.g. "4.00 m vs 6.00 m minimum"), with a reminder that Special Permission applies. (5) When FAR is reached before the storey cap, the calculator returns the lower storey count and the design envelope explains why — the FAR ceiling is binding, not the storey cap. The worked examples below cover each.

What the calculator does not include

Setbacks for front, side, and rear yards vary by road class and neighbouring use; they are tracked by a separate UDA schedule and merit their own tool. Coastal Conservation Department overlays, Central Cultural Triangle and archaeological reserves, Special Project / high- rise approval above the storey cap, and parking-bay schedules are all out of scope for v1. For the LKR cost of lodging the approval application, use the Sri Lanka building approval fee calculator. For unit conversion across perches, square metres, and square feet, use the Sri Lanka land area converter.

Important. These are the maximum legal limits per the UDA Schedules of Planning Standards. Actual approval depends on site-specific factors (archaeological, coastal, environmental, road reservation). Always confirm with your local authority's planning officer before purchase or design lock-in.

Three scenarios that exercise the FAR / coverage / storey interactions and the corner-plot uplift. Try plugging each set of inputs into the calculator above — the result tiles should match the numbers below to the second decimal place.

• Urban Development Authority — Planning Standards & Regulations
• UDA — Development Plans (Colombo, Kandy, Galle, Negombo, Matara)
• Survey Department of Sri Lanka — official conversion table

Quick reference — UDA national defaults applied by this calculator:

• Primary Residential: FAR 1.25× · 55% coverage · 2 storeys · frontage ≥ 4.5 m
• Secondary Residential: FAR 2.00× · 60% coverage · 3 storeys · frontage ≥ 6.0 m
• Mixed Residential: FAR 3.00× · 65% coverage · 4 storeys · frontage ≥ 6.0 m
• Mixed Commercial: FAR 5.00× · 75% coverage · 6 storeys · frontage ≥ 9.0 m
• Commercial / CBD: FAR 8.00× · 80% coverage · 12 storeys · frontage ≥ 12.0 m
• Industrial: FAR 2.50× · 60% coverage · 4 storeys · frontage ≥ 9.0 m

Zone parameters were last cross-checked against the UDA Schedules of Planning Standards on 2026-05-17. The page is reviewed whenever the UDA gazettes an amendment.