What clearance height do I need for a bridge over railway track?

UK standard loading gauge clearance is 4720mm (15 feet 6 inches) above rail level. In OO gauge this is approximately 62mm. In N gauge it is about 32mm. Always add a few mm for safety and to allow for any track height variations.

How wide should a bridge opening be?

For a single track in OO gauge, the minimum opening width is about 42mm (3200mm / 76). For double track, allow 80-85mm. Add wall thickness (5-10mm each side) for the bridge structure itself.

What materials can I use for model bridges?

Card and balsa wood for scratch-building. Styrene sheet for clean modern structures. Plaster for stone bridges. Commercial kits from Ratio, Wills, Metcalfe (card), and Peco cover most common UK bridge types. Laser-cut wood kits are also excellent.

How do I model bridge abutments?

Abutments are the supports at each end of the bridge. They must be wide enough to support the deck and tall enough for the required clearance. In OO gauge, build from stacked card, plaster blocks, or commercial stone-effect sheets. Embed them into the scenery for a realistic look.

ModelCalcs

Bridge Calculator — Span, Clearance & Approaches

Size bridges for your layout with correct span, clearance height and approach grades.

Gauge

Bridge Type

Number of Tracks

Span Length (mm)

How We Calculate This

Calculates bridge clearances based on UK loading gauge standards, scaled to your chosen gauge.

Formula

Clearance height = 4720mm (UK standard) / Scale ratio
Clearance width = (3200mm / Ratio) x Track count
Total length = Span + (2 x Approach length)

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify quantities before purchasing materials.