Austin code calculators: FAR, impervious cover, setbacks, trees and more

Last verified August 6, 2026 against the Austin Land Development Code · Kimbrough Gray · KiliGray Homes

Ten calculators covering the numbers Austin projects turn on: floor area, impervious cover, setbacks and setback planes, tree protection and critical root zones, compatibility height, multifamily density, sidewalk triggers and critical water quality zone widths.

Applies to: Each calculator states its own scope. Several apply only to particular districts, lot sizes or watersheds, and each links to the page explaining when it applies.

How to use these

Each calculator below is the same tool that appears on the page explaining the rule behind it. Every figure comes from a single tested source, so the answer here and the answer on the topic page can never disagree.

None of them is a substitute for reading the rule. Each one links to the page that sets out when it applies, what it excludes, and where the code defers to a criteria manual we cannot compute for you.

Floor area (FAR)

Maximum floor area for a lot under Subchapter F, including the small lot regime and the minimum allowance. Full explanation on floor-to-area ratio.

Lot size sq ft Dwelling units Inside the Subchapter F boundary

Impervious cover

How much of a lot may be covered by hard surfaces, by zoning district. Watershed and overlay limits can be lower and govern where they are. See impervious cover.

Lot size sq ft Zoning district

Setbacks

The four setback figures, which depend on base district, use and whether the lot is a small lot. See setbacks.

Base district Use Lot Small lot zoning Flag lot Adjacent to an alley Street level

Setback plane (the tent)

How tall you may build at a given distance in from the side lot line, and the point beyond which extra distance buys no more height. See the tent.

Distance in from the side lot line ft Inside the 100-year floodplain Use the 2.6.D alternative plane First floor wall plate height ft

Tree protection and root zones

Whether a tree is protected or heritage, and the critical root zone it carries. See trees.

Trunk diameter inches Species

Compatibility height and buffers

Height limits imposed by proximity to a triggering property, and whether a compatibility buffer is required. See compatibility.

Distance to the triggering property ft Your base zoning height limit ft Dwelling units on the site Site width from the shared line ft Residential uses only

Multifamily density

How many units a multifamily site yields, derived from minimum site area per dwelling unit. See multifamily districts.

Site area sq ft District Unit type

Critical water quality zone width

How wide the zone is, by watershed classification and waterway class. See critical water quality zones.

Watershed classification Waterway Drainage area acres Reduction applied

Slope gradient

Rise over run as a percentage, and which of the 15%, 25% and 33% thresholds you land in. See slopes, cut and fill.

Rise ft Run ft

Commercial district envelope

Height, setbacks, coverage, impervious cover and floor area for the eight commercial districts. See commercial districts.

District Lot size sq ft

Where a calculator gives a range, that is the code's range. Several critical water quality zone boundaries follow the 100-year floodplain, with the figures acting only as a floor and a ceiling on that line. Collapsing those to a single number would be inventing precision the ordinance does not have.

Common questions

Are these Austin code calculators official?

No. They are our own tools, built from the cited code sections and kept in a single tested module. They are a starting point for a conversation with the city, not a substitute for a review.

Why does a calculator sometimes give a range instead of a number?

Because the code does. Several critical water quality zone boundaries follow the 100-year floodplain, and the figures in §25-8-92 are only the minimum and maximum distances from the centerline. The exact line comes off the floodplain map.

Do the calculators account for overlays and watershed limits?

Not automatically. Each states its own scope. A zoning impervious cover limit, for instance, can be overridden by a lower watershed, overlay or Barton Springs Zone limit, and the lower figure governs.

Send us an address and we will tell you what we find

We do this research ourselves on every project we take on — zoning, floodplain, watershed, trees, whether it is a legal lot. Send us an address and we will run it and tell you what we find. It works the same whether you own a vacant lot, a house you are thinking of adding a unit to, or a house you are thinking of replacing. No charge and no strings, and if it is a bad lot we will say so.

Send us an address

We are homebuilders, not the City of Austin. This page explains how we read the code in practice — it is not legal advice and it is not an official determination. Always confirm with Austin Development Services before you rely on it for a project. The authoritative text is the Austin Land Development Code; permitting questions go to Austin Development Services Department.