Planning
Density is measured in the wrong units almost everywhere
Dwellings per hectare tells you nothing about how many people are there, how much floorspace exists, or what the place feels like.
Comparisons of measuring density usually pick a winner. This one picks the circumstances, which is more useful.
The difference in one place
- Dwellings per hectare ignores dwelling size and household composition.
- Net and gross density can differ by a factor of two on the same site.
- Floor area ratio describes built volume but not the form it takes.
Dwellings are not people
A hundred one-bedroom flats and a hundred family houses count identically in dwellings per hectare and house very different numbers of people. Household sizes have fallen in most countries over decades, so a district can lose population while gaining dwellings.
This is a large part of why inner areas of many older cities house fewer people today than a century ago despite intensive development. Any density policy expressed in dwellings is measuring the wrong quantity for almost every purpose it is used for.
Net and gross are quietly different
Net density measures dwellings against the developable plot; gross density includes roads, parks, schools and everything else. The two can differ by a factor of two, and policy documents frequently fail to say which they mean.
At street level, comparisons between schemes, districts or cities are therefore unreliable unless the basis is stated. This is a routine source of confusion in planning debate and it is entirely avoidable.
Floor area ratio describes volume, not form
The ratio of built floor area to plot area captures how much building exists and says nothing about its shape. The same ratio can produce a uniform six-storey block covering most of the plot or a slender tower in open ground. Those two options produce completely different streets, microclimates and management costs.
On the ground, using floor area ratio alone as a policy lever therefore leaves the most consequential decision unregulated.
Perceived density tracks form, not numbers
People routinely describe well-proportioned dense districts as pleasant and lower-density tower estates as overcrowded. What drives the perception is enclosure, street width to building height ratio, activity at ground level and the quality of shared space. This mismatch between measured and perceived density explains much of the public opposition that surprises planners.
Arguing about numbers with people who are describing a feeling is a reliable way to lose the argument.
The useful measures are the boring ones
Population per hectare, floor area per person, plot coverage and building height together describe a place adequately. Adding street frontage per hectare and open space per person covers most of what remains. None of these are difficult to calculate from data most planning authorities already hold.
The obstacle is that policy is written in inherited units and changing them invalidates every historic comparison.
What works in a dense grid may not transfer to a low-density suburb.
Density policy targets the wrong end
Minimum density requirements aim to prevent land waste and can be met by building many small units. Maximum density limits aim to control impact and are frequently the binding constraint on housing supply near transit.
Measured properly, both would work better expressed as built form standards — height, coverage, frontage, depth — which regulate the outcome directly. Form-based codes take this approach and are used in a growing number of jurisdictions with mixed but generally positive assessment.
Side by side
| Consideration | What it means in practice |
|---|---|
| Dwellings are not people | Dwellings per hectare ignores dwelling size and household composition. |
| Net and gross are quietly different | Net and gross density can differ by a factor of two on the same site. |
| Floor area ratio describes volume, not form | Floor area ratio describes built volume but not the form it takes. |
The takeaway
Ask how many people live there and how much space each of them has. The rest is bookkeeping.
Measure the walk, not the map.
Questions readers ask
Is high density bad for quality of life?
Evidence links dissatisfaction to specific attributes — noise, lack of daylight, poor management, absence of open space — rather than to density itself. Many of the most desirable urban districts are very dense.
What is floor area ratio?
Total built floor area divided by plot area. A ratio of three means three square metres of floorspace for every square metre of site, achievable as three full-coverage storeys or six storeys on half the plot.
