Start from the format
The catchment is a statement about how far someone will travel for what you sell. Frequency and ticket size drive that distance: people walk five minutes for coffee and drive forty for a homewares warehouse.
- Convenience, coffee, pharmacy, walk-in services — 0.5–1 km in dense urban, 1–2 km suburban.
- Supermarket, QSR, fitness, childcare — 1–3 km suburban, up to 5 km in low density.
- Large-format retail, hardware, furniture — 3–5 km urban, 5–10 km regional.
- Destination, regional centres, entertainment — 10–20 km, sometimes more in rural markets.
Then adjust for density
Density does more work than format. A 1 km radius in an inner-city apartment precinct can contain 40,000 residents; the same 1 km on a semi-rural arterial might contain 900. The radius is a means to a population, and it is the population that has to make sense.
A useful reframing: decide roughly what resident population the format needs to be viable, then choose the radius that delivers it in that density. Run two or three radii around the same point and compare — that is a cheap way to see the density gradient around the site.
Keep it constant when you are comparing sites
If you are ranking candidate sites, the catchment size must be identical across all of them, even where it flatters one and penalises another. Varying the radius per site to make each look reasonable destroys the comparison entirely.
Screen with one fixed radius, shortlist, and only then run bespoke catchments on the two or three finalists.
The sanity checks
Four quick tests catch most sizing mistakes before they reach a paper.
- Barrier test — does the ring cross water, a motorway with no crossing, a rail corridor or a ridge? If yes, the count is inflated.
- Competitor test — does the ring extend past an established competitor? Customers past that point are mostly theirs.
- Population plausibility — is the resident count within the normal range for this format? If it is triple the usual, the radius is too big.
- Sensitivity test — how much does the population change between the radius you picked and one step smaller? A large swing means the result depends on your choice, so state the assumption explicitly.
What we support
Reports use radius catchments from 0.5 km to 20 km, which covers everything from a walk-in urban format to a regional destination site. Radius keeps every site directly comparable and every figure reproducible — see the radius vs drive-time comparison for why that matters when the number ends up in a lease or credit paper.