Floor Area Ratio Calculator
Free Floor area ratio Calculator for home & garden projects. Enter dimensions to get material lists and cost estimates.
Reviewed by Abdullah, Technical Content Specialist
Formula
FAR = Total Floor Area / Lot Area
Divide the total floor area of all stories by the gross lot area. Both values must be in the same units (square feet or square meters). The result is a dimensionless ratio. A FAR of 0.5 means the building contains half as much floor space as the lot area. Lot coverage is calculated separately as the building footprint (floor area divided by number of stories) divided by the lot area.
Worked Examples
Example 1: Two-Story House on Standard Lot
Problem:Calculate FAR for a 2-story house with 2,500 sq ft per floor on a 10,000 sq ft lot.
Solution:Total floor area = 2 x 2,500 = 5,000 sq ft\nFAR = 5,000 / 10,000 = 0.50\nLot coverage = 2,500 / 10,000 = 25%\nOpen space = 10,000 - 2,500 = 7,500 sq ft (75%)
Result:FAR = 0.50, Lot Coverage = 25%
Example 2: Mixed-Use Commercial Building
Problem:Calculate FAR for a 5-story building with 8,000 sq ft per floor on a 20,000 sq ft lot.
Solution:Total floor area = 5 x 8,000 = 40,000 sq ft\nFAR = 40,000 / 20,000 = 2.00\nLot coverage = 8,000 / 20,000 = 40%\nOpen space = 20,000 - 8,000 = 12,000 sq ft (60%)
Result:FAR = 2.00, Lot Coverage = 40%
Frequently Asked Questions
What is Floor Area Ratio (FAR) and why does it matter?
Floor Area Ratio is the total building floor area divided by the gross lot area. It is a key zoning and urban planning metric that controls building density on a parcel. A FAR of 1.0 means the total floor area equals the lot size, which could be a one-story building covering the entire lot or a two-story building covering half. Municipalities use FAR limits to manage neighborhood density, traffic, parking needs, and infrastructure capacity.
What floor areas are included in FAR calculations?
FAR typically includes all enclosed floor space measured to the exterior face of walls, including habitable space, hallways, stairwells, and mechanical rooms on every floor. Most jurisdictions exclude parking garages (especially underground), unenclosed balconies, rooftop mechanical equipment, and cellar space below grade. Some cities also exclude ground-floor retail in certain zones or provide FAR bonuses for green building features. The exact inclusions and exclusions vary by local zoning code.
References
Reviewed by Abdullah, Technical Content Specialist · Editorial policy