Parliament Hinge Sizes: Standard UK Options

Parliament hinge sizes matter whether you are fitting new French doors, upgrading casement windows or replacing old hardware on a period property. A parliament hinge is a specialised hinge that gives extra clearance between the door or window and the frame; this allows the leaf to swing clear of architrave and trim so the opening can reach 180 degrees or more. Choosing the correct size, material and fixing method will determine how well the assembly performs for decades.

What defines a parliament hinge

Unlike a standard butt hinge, a parliament hinge has an offset knuckle and one or both leaves are cranked so the hinge projects the door or sash away from the frame. That projection is the key feature: it prevents the leaf from hitting skirting or mouldings when opened fully. Parliament hinges are commonly used on external doors, French doors, patio doors and tall casement windows where full opening is required.

How sizes are specified

Hinge size is usually given as the length of each leaf: the imperial inch value is still the most common way to describe sizes in UK trade. For example, a 4 inch parliament hinge describes leaves of approximately 4 inches (about 102 mm). Sizes are measured with the hinge open at 180 degrees; the dimension runs from end to end of the leaf. Other important dimensions to check on a datasheet are the projection (how far the hinge sets the door from the frame), knuckle diameter and the screw hole centres.

Standard UK parliament hinge sizes

Common sizes stocked by trade suppliers and builders’ merchants include the following; choose the size that matches the door height, weight and aesthetics:

• 3 inch (about 76 mm): used for lightweight internal doors and small casement windows
• 3.5 inch (about 89 mm): common for lighter single doors and some narrow French doors
• 4 inch (about 102 mm): the most common choice for domestic entrance and internal doors
• 5 inch (about 127 mm): used for heavier doors and wider leaves where extra bearing surface is useful
• 6 inch (about 152 mm): suited to tall, heavy doors and commercial applications

Trade professionals will often select the smallest hinge that gives adequate screw pull-out resistance and bearing length; larger hinges distribute load better and are preferable for heavy doors.

Selecting material and finish

For external doors and exposed windows choose corrosion-resistant options: stainless steel (A2 for most external use; A4 for coastal locations) or heavily lacquered/brass finishes. For internal doors you can use brass, steel or coated variants in chrome, satin chrome or black finishes to match ironmongery. For high-traffic doors consider ball-bearing parliament hinges to reduce friction and wear.

Practical trade tips

• Number of hinges: standard residential doors up to 2.1 m usually take three hinges; heavier or taller doors and French doors may need four; use hinge load ratings on manufacturer datasheets to decide.
• Security: for external doors use security screws or non-removable pins to protect against hinge-side attack. Consider bolt-through fixings into a reinforcing block where possible.
• Fixing screws: countersunk wood screws are normally used; typical sizes are No.8 or No.10, with lengths chosen to get good bite into the frame (25 mm to 40 mm penetration into the substrate for timber). In masonry or metal adapt appropriate plugs or self-tapping screws.
• Check projection: if you have deep architrave or handles that protrude, confirm the hinge projection on the datasheet to ensure clearance.
• Material matching: pair hinge finish with handles and locks to avoid galvanic corrosion and visual mismatch.

DIY installation guidance

Fitting a parliament hinge can be tackled by a confident DIYer; for heavy or fire doors call a trade fitter. Follow these steps for a safe installation:

• Measure and mark: measure leaf positions from top and bottom; typical spacing is 150 mm from top and bottom edges with the third hinge evenly spaced; always check manufacturer recommendations.
• Transfer template: use the hinge as a template and mark the outline on door and frame. Some parliament hinges are surface-mounted and need no mortice; many require a shallow mortice to sit flush.
• Cut the mortice: chisel or router carefully to the depth of the hinge leaf; keep the rebate neat so the hinge sits square and true.
• Pilot holes: drill pilot holes for screws to prevent splitting timber; countersink where required so screws sit flush.
• Fixing and alignment: fit the hinge to the frame first, then offer the door and fix the second leaf. Use packers behind the hinge if needed to achieve correct reveal and alignment.
• Final checks: open and close the door to check for binding; adjust the hinge position if the door sticks or gaps are uneven. Light lubrication of the knuckle with a few drops of light machine oil helps smooth operation.

Common problems and troubleshooting

If the door scrapes or will not close squarely, check that the hinge mortices are the same depth and that the screws are tight. Sagging doors indicate inadequate fixings or insufficient number of hinges; upgrading to a larger hinge or adding a fourth hinge can correct sag. For exterior applications where hinges stiffen in cold weather, choose stainless steel or ball-bearing versions and keep the knuckle lubricated.

Where to get more technical data

Always consult the hinge manufacturer’s datasheet for exact dimensions: leaf length, projection, knuckle diameter and fixing hole centres. For trade professionals, ordering from a supplier who provides CAD drawings and load capacity charts will speed specification and installation. If working on a listed building check conservation requirements before changing visible ironmongery.

Recommended Products

Based on this article, you may find these products helpful:

• Patio Door Handle Set - 92PZ White
• Winlock Patio Door Handle Set
• Pembroke Locking And Dummy Patio Door Handle
• Top-Hung Window Hinge - Standard
• Side-Hung Window Hinge - Standard

Conclusion: next steps

Choosing the correct parliament hinge size comes down to matching leaf length, projection and material to the door or window weight and the surrounding trim. For most UK domestic doors a 4 inch parliament hinge is a sensible default; lighter or heavier situations call for smaller or larger sizes respectively. Next steps: measure the door and frame, consult product datasheets for projection and load capacity, and if in doubt seek advice from the Window Hardware Store trade team or download technical sheets from the pillar page at /guides/door-hinges. For DIYers, practice on a spare piece of timber first and use correct pilot screws and morticing to achieve a neat, long-lasting result.