Net Lettable Area Calculator
Net lettable area from gross floor area — the cores, plant, lobbies and walls that come out — and the efficiency ratio that tells you whether a floor plate is any good.
Gross floor area is everything inside the external walls.
How the net lettable area calculator works
Gross floor area is everything inside the external walls. Net lettable area is what a tenant pays for, after lift cores, stairs, plant, lobbies and structure. The ratio between them is the building's efficiency, and it is the single number a leasing agent asks first.
Eighty to eighty-five per cent is good for offices; towers with big cores fall to 75. A few points of efficiency is worth more than most façade decisions.
Formula: NLA = GFA − cores − plant − lobbies − structure; efficiency = NLA / GFA
Worked examples
| Inputs | Net lettable area (m²) | Note |
|---|---|---|
| An 1,800 m² floor | 1,438 | 80% efficient |
| A tower with a big core | 1,288 | below 75% |
| A lean plate | 1,556 | above 85% |
FAQFrequently asked questions
What is net lettable area?
The floor area a tenant actually occupies and pays for — gross area less cores, plant, lobbies and structure. Definitions vary slightly by measurement standard.
What is a good efficiency ratio?
Eighty per cent and above for offices. Towers pay for their height with bigger cores and often sit at 75; low-rise plates can exceed 88.
Why does a few per cent matter?
Because it is a few per cent of the rent, every year, for the life of the building. A 3-point efficiency gain is worth more than most finishes.
How do I improve efficiency?
A bigger floor plate for the same core, scissor stairs, and services in the ceiling void rather than in rooms. Core design is the lever.
Is NLA the same as net internal area?
Close, but the measurement standards differ in how they treat columns and partitions. Use the one your market leases on.
Where these figures come from
- Sabine (1922) — Collected Papers on Acoustics — the reverberation-time equation
- CIBSE Guide A — Environmental design — daylight, comfort and ventilation criteria
- Neufert — Architects' Data — the standard reference for space and dimension
- International Code Council — International Building Code — occupant load and egress factors
- Building Regulations — Approved Documents — the UK building regulations
Last checked: September 2026. Formulas are the standard building-science and code relationships; default thresholds are common international values and should be replaced with the ones in your code.