How much bearing does a lintel need?

The standard minimum bearing for a steel lintel is 150mm each side of the opening. This means a 1200mm wide opening needs a lintel at least 1500mm long (1200 + 150 + 150). Some heavy-duty lintels or wider openings may require 200mm or more bearing. Always check the manufacturer's installation guide.

What type of lintel do I need for a cavity wall?

For a standard UK cavity wall, you need a combined cavity wall lintel that spans both the inner and outer leaf (e.g. Catnic CG90/100 or IG L1/HD 100). These come with an integral damp-proof tray. The lintel must suit your specific cavity width — typically 50mm, 75mm, or 100mm.

Do I need Building Regulations approval to install a lintel?

Yes, replacing or installing a lintel is structural work and requires Building Regulations approval. If you are creating a new opening in a load-bearing wall, you will also need a structural engineer's calculation to specify the correct lintel. Building Control must inspect before the opening is made permanent.

What is the maximum span for a standard steel lintel?

Standard domestic steel lintels (Catnic, IG Lintels) are available in lengths up to about 4800mm. However, the maximum clear span depends on the load and lintel duty. For openings wider than about 2.4m with significant loads, a structural engineer should specify the lintel size and type.

Can I use a concrete lintel instead of steel?

Yes, precast concrete lintels are still used, particularly for internal walls and smaller openings. They are cheaper but heavier and have lower load capacity than steel lintels of the same depth. For cavity walls, steel lintels with integral DPC trays are strongly preferred to prevent cold bridging and damp issues.

Lintel Sizing Calculator — What Size Lintel Do I Need UK?

Lintel Sizing Calculator — What Size Lintel Do I Need?

Work out the minimum lintel length for your opening and get guidance on lintel type based on wall construction and load conditions.

Opening Width

Clear width of the door or window opening

Bearing Length (each side)

Min 150mm standard; 200mm for heavy loads

Wall Type

Construction type of the wall

Load Condition

What loads bear on the wall above the opening

Lintel Price (optional)

Enter the price of the lintel for your records

How We Calculate This

This calculator determines the minimum lintel length by adding the required bearing length to each side of the opening width. It then provides guidance on suitable lintel types based on your wall construction and loading conditions.

The formula

Minimum lintel length = Opening width + (Bearing × 2)

For example, a 1200mm opening with 150mm bearing each side needs a lintel at least 1500mm long. We then recommend the nearest standard manufactured length.

Lintel type guidance

Our recommendations reference common UK lintel ranges from manufacturers such as Catnic and IG Lintels. The correct lintel depends on:

Wall type (single leaf, cavity, or solid)
Load condition (roof only, floor + roof, multi-storey)
Opening width (wider = heavier duty lintel)
Cavity width (for cavity wall lintels)

Important disclaimer

This calculator provides general guidance only. Lintel selection for structural openings must be confirmed by a structural engineer and approved by Building Control under the Building Regulations (Approved Document A). This is particularly important for load-bearing walls, wide openings, and multi-storey buildings.

Frequently Asked Questions

Last updated: February 2026

All calculations are estimates. Verify with your supplier.

Lintel Sizing Calculator — What Size Lintel Do I Need?

How We Calculate This

The formula

Lintel type guidance

Important disclaimer

Frequently Asked Questions

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