I’ve been writing about commercial property for years, and one question keeps coming up from business owners: “How do I know if the space is actually big enough for what I need?” It sounds simple, but the answer is rarely straightforward. The way commercial property is measured in the UK follows strict professional standards set by the Royal Institution of Chartered Surveyors (RICS), and if you don’t understand the difference between the various measurement methods, you can easily end up paying for space you can’t actually use. Nearly all commercial property in the UK is priced and measured to these RICS standards, so knowing what you’re looking at on a floor plan is the first real step toward a sound business decision.
That 80 to 100 square feet per employee figure is a good starting point, but it only tells part of the story. You also need to account for meeting rooms, kitchenettes, storage, and circulation space — the corridors and walkways that eat up square footage without housing a single desk. I’ve seen too many tenants sign up for a space that looks generous on paper, only to discover half of it is unusable because of awkward pillar placement or narrow corridors. The trick is learning to read a floor plan the way a surveyor does, and that starts with understanding the two most common measurement terms you’ll encounter. Here’s what you actually need to know.
If you’re just starting your search, it’s worth reading up on the full process of renting commercial property before you begin viewing spaces. And if you’re unsure about any legal terms in your lease, speaking with a tenant landlord lawyer early on can save you from costly misunderstandings later.
Understanding Net Internal Area and Gross Internal Area on a Floor Plan
The single most important thing you can do when evaluating a commercial floor plan is to identify whether the quoted figure is Net Internal Area (NIA) or Gross Internal Area (GIA). These two measurements can differ by 10% or more on the same property, and landlords don’t always lead with the one that benefits you. NIA is the usable area inside the building — the space where you can actually put desks, stock, or machinery. It excludes structural walls, corridors, stairwells, and shared amenities. GIA, on the other hand, is the total area measured to the inside of the external walls, including internal pillars, toilets, and loading bays. If a landlord quotes GIA but you’re thinking in terms of usable space, you’re setting yourself up for a nasty surprise when you try to fit your team in.
My advice is always to ask the agent or landlord for the NIA figure in writing before you even book a viewing. If they hesitate or try to steer you toward GIA, that’s a red flag. I’d also recommend bringing a tape measure to the viewing and spot-checking a few key dimensions against the floor plan. You’d be surprised how often the plan doesn’t match reality. For a deeper look at what can go wrong with location claims and floor plans, have a read of this guide on spotting hidden pitfalls in office space.
Why Getting the Floor Plan Right Affects Your Bottom Line
Getting the floor plan wrong doesn’t just mean a cramped office — it means paying for space you can’t use, and potentially signing up for costs you didn’t budget for. Take business rates, for example. These are a statutory tax collected by local councils based on a property’s rental value, as assessed by the Valuation Office Agency (VOA). The 2026 Business Rates Revaluation took effect on 1 April 2026, so the rateable value of your property may have changed recently. If your floor plan shows a larger area than you actually occupy, you could be paying higher rates than necessary.
Consider this scenario: you’re a small marketing agency looking for office space for a team of eight. Using the 80–100 sq ft per person benchmark, you need roughly 640–800 sq ft of NIA. You find a property quoted at 950 sq ft GIA. That sounds like plenty, but after subtracting structural walls, a central pillar, and a shared corridor, the NIA might be only 700 sq ft — barely enough for your team with no room for growth. If you’d signed a three-year lease without checking, you’d be stuck paying for space you can’t use and facing the cost of moving or subletting.
What I tend to notice is that first-time commercial tenants often overlook the VAT issue entirely. Commercial rents are almost always quoted exclusive of VAT. If the landlord is VAT-registered, an additional 20% is added to your rent and service charges. If your business isn’t VAT-registered, you can’t reclaim that, turning it into a direct 20% increase in your overheads. That’s a significant cost that won’t show up on the floor plan but will hit your bank account every quarter. For more on the financial surprises that can arise, check out this breakdown of hidden costs in commercial leases.
Where Tenants Misread Floor Plans and Get Stung
I’ve seen the same mistakes repeat themselves across dozens of lease negotiations. Here are the most common ones, and how to avoid them.
Confusing NIA with GIA when comparing properties
This is the biggest one. You see two properties: one quoted at 1,200 sq ft and another at 1,000 sq ft. The larger one seems like the better deal, but if the 1,200 sq ft figure is GIA and the 1,000 sq ft is NIA, the smaller property might actually offer more usable space. Always ask for both figures and compare like-for-like. A tenant landlord lawyer can help you ensure the lease accurately reflects the agreed measurement.
Ignoring the space buffer for growth
If you’re signing a multi-year lease — and commercial leases often run 3 to 15 years or more — you need to factor in an extra 15% to 20% space buffer for projected business expansion. A team of five today could be a team of eight in two years. If your floor plan doesn’t have the capacity to absorb that growth, you’ll be looking for new premises long before your lease is up, which comes with its own costs and disruption.
Overlooking the minimum workspace volume requirement
UK workplace regulations require a bare minimum workspace volume of 11 cubic metres per person. That’s not just floor area — it’s floor area multiplied by ceiling height. A space with low ceilings or mezzanine levels might meet the square footage requirement but fail the volume test. This is especially relevant in converted buildings or basement offices. Measure the ceiling height and do the calculation before you commit.
Not checking the planning use class
The floor plan might look perfect, but if the property’s planning use class under the Town and Country Planning (Use Classes) Order 1987 doesn’t match your intended use, you could be in breach of planning law. Many high street uses now fall under Class E, but not all. If you’re planning to run a hot food takeaway from a former retail unit, you may need planning permission. Always confirm the use class with the landlord or your solicitor before signing. For a detailed look at this, read this guide on permitted use clauses.
→ Scroll right to see all columns
| Measurement Type | What It Includes | What It Excludes |
|---|---|---|
| Net Internal Area (NIA) | Usable floor space, toilets, kitchenettes | Structural walls, columns, stairwells, corridors |
| Gross Internal Area (GIA) | Everything inside external walls, including pillars and loading bays | External walls, open balconies |
How to Read a Commercial Floor Plan Like a Pro
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Once you understand the measurement basics, you can start evaluating floor plans with confidence. Here’s a practical step-by-step approach.
Start with the NIA and calculate your headcount
Take the quoted NIA and divide by 80 to 100 to get a rough maximum headcount. For a team of ten, you need at least 800 sq ft of NIA. Then add 15% to 20% for growth if you’re signing a lease longer than two years. Don’t forget to account for meeting rooms, storage, and break areas — these aren’t luxuries, they’re operational necessities. A good rule of thumb is that desks should take up no more than 60% of your NIA, leaving the rest for circulation and shared spaces.
Check the dimensions against your equipment
Industrial units are a different beast entirely. They’re calculated by physical racking and equipment footprint rather than headcount. If you’re renting a warehouse or workshop, bring a scaled drawing of your largest pieces of equipment and overlay them on the floor plan. Make sure there’s enough clearance for forklifts, pallet trucks, and loading bays. A standard double garage is roughly 11.9 square metres or 128 square feet — use that as a mental benchmark when visualising smaller industrial spaces.
Verify the lease type and repair obligations
A commercial lease can be “inside” or “outside” the security of tenure provisions of the Landlord and Tenant Act 1954. If it’s inside, you have a right to renew at the end of the term, subject to certain grounds for refusal. If it’s outside, you have no automatic renewal right and must vacate unless you negotiate a new deal. Also check whether the lease is “full repairing and insuring” (FRI). Under an FRI lease, you’re responsible for all repairs and reinstatement, sometimes including pre-existing disrepair if you’re not careful. A photographic schedule of condition can limit your liability to “no worse than at commencement.”
Factor in business rates and empty property relief
Business rates are based on the property’s rateable value, which is reassessed by the VOA. The most common relief is Small Business Rates Relief, which can provide up to 100% relief for properties with a rateable value under £12,000. Eligible businesses in certain sectors can qualify for significant discounts, such as 40% off their bills. Charities and Community Amateur Sports Clubs (CASCs) can receive up to 80% mandatory relief. And if the property is empty, you’re generally exempt from paying rates for the first three months. Don’t assume you’ll qualify for relief — check with your local council or a business rates specialist. For more on managing ongoing costs, see this guide on service charges.
- 1Get the NIA in writingAsk the agent or landlord for the Net Internal Area before viewing. Compare it to the GIA to understand how much space you’ll actually lose to walls and corridors.
- 2Calculate your headcount and growth bufferDivide the NIA by 80–100 for office space. Add 15–20% for growth if signing a multi-year lease. Account for meeting rooms, storage, and break areas.
- 3Check the lease type and repair termsConfirm whether the lease is inside or outside the 1954 Act. If it’s FRI, insist on a photographic schedule of condition to cap your repair liability.
- 4Verify business rates and relief eligibilityCheck the rateable value with the VOA. Ask about Small Business Rates Relief, sector-specific discounts, and empty property relief before you sign.
Frequently Asked Questions
Can I use a laser measure to check the floor plan myself? ▾
What happens if the floor plan in the lease doesn’t match the actual property?
Do I need a surveyor to measure the property?
Are there different measurement standards for retail vs office space?
Can I sublet part of my space if the floor plan shows extra room?
Sources and Further Reading
Best practices for leasing event venues in the UK — If you’re considering a specialist property type, this guide covers the unique considerations for event spaces.
The UK’s most underrated cities for commercial space opportunities — Looking beyond London? This article highlights cities where you might find better value and more flexible lease terms.
Guide to renting commercial property. Omeeto, 2025.
Essential tips for successfully renting a commercial property in the UK. Fraser Bond, 2025.
How to rent a commercial property in the UK. Sprintlaw, 2025.
