A mezzanine floor load rating is the uniformly distributed imposed load the deck is designed to carry, stated in kilonewtons per square metre (kN/m²). Typical ratings run from about 3.5 kN/m² for offices to 4.8 kN/m² for light storage and 7.2 to 9.6 kN/m² or more for heavy storage and machinery, which is roughly 357 to 979 kg spread over every square metre.

The rating is the most important number in a mezzanine specification. It decides the size of every joist, beam, column and baseplate, and it limits what the floor can be used for over its whole life. This guide explains what the number means and how to pick one.

What does a mezzanine load rating mean?

A load rating describes the imposed load: the weight of people, goods, shelving and equipment that the floor can carry in addition to its own weight. Engineers call the floor's own weight the dead load and the imposed load the live load. The rating is stated as a uniformly distributed load (UDL), which assumes the weight is spread evenly over the whole deck area.

In the UK, imposed floor loads are set out in Eurocode 1, BS EN 1991-1-1, used with its UK National Annex. BSI lists the current National Annex as NA to BS EN 1991-1-1:2025 (BSI Knowledge). Approved Document A, the statutory guidance on structure, expects the floor to carry its dead and imposed loads safely without overloading the building (GOV.UK, Approved Document A). The mezzanine designer takes the rating you specify, adds the dead load and the safety factors in the design code, and sizes the steel from there.

Typical load ratings by use

Most UK mezzanines are specified at one of a small number of standard ratings. Published guidance from the Northamptonshire Chamber of Commerce gives 3.5 kN/m² as the minimum for office use, 4.8 kN/m² for light storage, 4.8 to 7.2 kN/m² for storage and material handling, and 9.6 kN/m² or more for heavy storage and machinery (Northamptonshire Chamber of Commerce).

Typical use	Rating (kN/m²)	Approx. kg per m²	Comment
Offices, personnel	3.5	357	Light partitions, desks, people
Light storage	4.8	489	Boxed goods on hand-loaded shelving
Medium storage	7.2	734	Dense stock, archive, some pallets
Heavy storage, machinery	9.6+	979+	Pallet storage, production equipment

Office ratings in particular vary between projects: Designing Buildings Wiki notes that UK offices were long designed and marketed at 3.5 to 4.0 kN/m², and argues that lower figures can suit ordinary office floors (Designing Buildings Wiki, Floor loading). On a mezzanine, the extra margin is usually worth keeping. The kilogram figures in the table use the exact conversion. Some suppliers round to 100 kg per kN, which is why you may also see a 4.8 kN/m² floor described as 480 kg/m².

How to convert kN/m² to kg/m²

Divide by gravity. One kilonewton is the weight of about 102 kg on Earth (1,000 ÷ 9.81), so multiply a rating in kN/m² by 102 to get kg/m². To go the other way, multiply the mass in kg by 9.81 and divide by 1,000 to get kN.

Quick worked example

A run of shelving holds 2,000 kg of stock over a 10 m² area of deck including its aisle. That is 2,000 × 9.81 ÷ 1,000 ÷ 10, or about 2.0 kN/m² averaged over the area. Add people and a pallet truck moving through, and a 3.5 kN/m² floor may be fine on average. The catch is that loads are rarely even, which is where point loads come in.

Why point loads matter more than the average

A UDL rating assumes the load is spread evenly; real loads are not. A pallet concentrates its weight on a 1,200 × 1,000 mm footprint. Shelving delivers its whole bay load through four small feet. A pallet truck puts most of the load through two small wheels. The deck boards and joists must carry these concentrated loads locally, even when the average across the floor is well inside the rating.

The chart below shows the pressure directly under a single UK pallet of different weights. A 1,000 kg pallet produces about 8.2 kN/m² under its footprint, more than a 7.2 kN/m² rating, even though one pallet on a large floor is light on average.

This does not always mean the floor is overloaded, because the designer can check the boards, joists and beams for the actual point and line loads. It does mean you must tell the designer about pallets, shelving and machines, with their weights and footprints, rather than quoting a single kN/m² figure. Heavy shelving on a deck behaves rather like racking on a slab: our guide to working out pallet racking beam capacity covers the same idea of matching each load path to the weights it carries.

How to choose the right rating

Choose for the heaviest realistic use over the floor's life. Changing the use of a mezzanine later, for example from offices to stock, can overload a floor that was perfectly safe when installed. The Northamptonshire Chamber guidance notes that office mezzanines are often specified at 4.8 kN/m² so they can be used for light storage later.

Work through these questions before you request quotes:

• What will be stored, and what is the heaviest full shelf bay or pallet?
• Will pallets be placed on the deck, and how many at once near the loading gate?
• Will pallet trucks, trolleys or machines run on the deck?
• Could the use change within the life of the lease or building?
• Is the existing floor slab known to be strong enough for the column loads?

A higher rating means heavier joists and beams, sometimes more columns and larger baseplates. The extra steel usually costs much less than strengthening or replacing a floor later; our article on what drives the cost of a mezzanine floor explains how the rating fits into the budget.

Showing and keeping to the rating

Once the floor is installed, its rating should be displayed where staff can see it, usually on a notice at the head of the stairs and at each loading point. Loading notices work the same way for racking; our guide to pallet racking load notices explains what a clear notice shows. The rating also matters to others: the Valuation Office Agency's Rating Manual asks valuers to record the load carrying capacity of mezzanine floors where possible (GOV.UK, Rating Manual).

Keep the design rating with the building's records. If anyone proposes a change of use, new machinery or pallet storage on the deck, the original designer or another engineer should check the floor against the new loads before the change is made. Our quality standards page explains the load data we supply with each order, and our structural mezzanine floor is designed to the rating and point loads you specify.

Frequently asked questions

What is the standard load rating for a mezzanine floor?

There is no single standard. Typical published ratings are 3.5 kN/m² for offices, 4.8 kN/m² for light storage and 7.2 to 9.6 kN/m² or more for heavier storage and machinery.

How many kg per square metre is 4.8 kN/m²?

About 489 kg per square metre, using 1 kN equals roughly 102 kg. Some suppliers round this to 480 kg per square metre.

Can I put pallets on a mezzanine floor?

Yes, if the floor is designed for them. Tell the designer the pallet weights, how many will stand at once and where, because a single pallet can create a local pressure above the floor's average rating.

Can a mezzanine load rating be increased later?

Sometimes, by adding columns, strengthening beams or changing the deck, but it needs an engineer's check and may need fresh building control approval. Specifying the right rating at the start is usually cheaper.

Sources

• Northamptonshire Chamber of Commerce: How to calculate how much weight a mezzanine floor can safely hold
• BSI Knowledge: NA to BS EN 1991-1-1:2025, UK National Annex to Eurocode 1
• GOV.UK: Structure, Approved Document A
• GOV.UK: Rating Manual, factories, workshops and warehouses
• Designing Buildings Wiki: Floor loading