Steel Gate Calculator — Frame, Hinges & Post Sizing

For pedestrian gates (up to 1m wide), 40x40x3 RHS is adequate. For single vehicle gates (up to 3m), 50x50x3 or 60x40x3 RHS is standard. For double gates (3-6m total) or tall gates (over 2m), 80x40x3 or heavier sections are needed. The frame must resist self-weight deflection (sag) and wind loading without excessive flex.

There is no code-mandated figure for steel gate post embedment, so the common trade rule of thumb is roughly one-third of the total post length below ground, with a practical minimum of about 600mm for pedestrian gates and 900-1200mm for vehicle gates. The post is set in a concrete foundation (C20/25 minimum, often C25/30 for heavy gates) — around 300mm square for pedestrian and 450mm square for vehicle gates. These are conventions, not regulated values; for tall, heavy, exposed or automated gates the post and foundation should be designed by a structural engineer to resist the actual overturning moment.

There is no British Standard for domestic steel-gate hinge selection, so these are fabricator rules of thumb — always confirm against the hinge manufacturer's published load table. As a guide, sized by per-leaf weight: under 50kg uses a 16mm pin / 150mm strap; 50-100kg a 20mm pin / 200mm strap; 100-200kg a 25mm pin / 250mm strap (ball bearing); over 200kg a 30mm pin / 300mm ball-bearing strap. Use 3 hinges for leaves over 100kg or over 2m tall. For heavy or automated gates have the hardware confirmed by a structural engineer.

This calculator does not size gate automation — it covers the gate weight, frame, hinges, posts and foundation only. For motorisation you would typically need: (1) a gate motor matched to leaf weight and length (ram or articulated-arm actuator for swing gates, rack and pinion for sliding gates); (2) safety devices to limit closing force, plus photocells and safety edges — the safety-in-use standard in the UK is BS EN 12453 (with BS EN 12604 for mechanical aspects and BS EN 12978 for safety devices); BS EN 13241 is the product/CPR standard; (3) an adequate power supply (230V or 24V with battery backup); (4) a manual release for power failure. In Great Britain powered gates are placed on the market under the Supply of Machinery (Safety) Regulations 2008 (UKCA). Note HSE issued a formal objection to BS EN 12453/13241 after powered-gate fatalities, so compliance with the standard alone is not sufficient — a full risk assessment is required, and the DHF codes of practice (TS 011 swing/sliding, TS 013 traffic barriers) are widely followed.

For UK external use, hot-dip galvanising (to BS EN ISO 1461) is essential for long-term durability. This can be left as-is (grey) or overcoated with powder coating for a colour finish (duplex system — 25+ year life). Alternatively, galvanise and apply two-pack polyurethane paint. Never paint raw steel without galvanising for external gates.