When landlords or their agents quote a total rent figure they will usually explain that it is X square feet at £Y per square foot. Then they will justify the number by giving you comparable figures for the amount per square foot that other tenants paid for similar premises in the area.
When landlords and tenants arrive at a consensus on the rent per square foot, what is often overlooked is checking how many square feet there actually are in the premises. This is potentially a bad mistake from the tenant’s point of view.
You need to make sure they not including the toilets.
They may have done external measurements, instead of interior measurements.
Sometimes, the landlords figures are just plain inaccurate. They may have been taken from a previous plan without being rechecked.
Even when the measurements are accurate, deciding the rent is not about merely discovering the exact floor area and multiplying it by a single rate per square foot. Shops, in particular, do not attract the same rate of rent per square foot for the back of the shop as for the front where the windows and most of the footfall are. Storage areas and basements should be charged at a completely different and lower rate. You need to make sure they not including the toilets (unless it’s a restaurant), or the cleaner’s cupboard, or any low height areas (e.g. the space under the stairs).
You could easily end up paying a significant percentage more rent than you really should do, simply by failing to have the property properly measured. Carrying out the measurement properly is a specialist task. Even when you have precise measurements, you still need to apply the correct rates to the different parts of the premises.