How much ballast do I need for OO gauge?

For OO gauge, the default ballast bed here is 30mm wide and 3mm deep. With loose crushed-granite ballast (bulk density roughly 1.5 g/cm³), a metre of single track works out at about 90-95g once the sloped shoulder profile is allowed for — so a typical 3-metre starter layout needs roughly 280-290g. Points and crossings need extra because their bed is wider. As a rough cross-check, a standard coffee mug (~300ml) of ballast covers around 3 metres of OO track.

What size ballast should I use?

For N gauge use fine ballast (under 1mm grain). For OO/HO use medium ballast (1-2mm grain). For O gauge use coarse ballast (2-3mm). Real ballast is 30-50mm, so divide by your scale ratio for the correct model grain size.

How do I fix ballast in place?

Spread dry ballast along the track, brush it into shape with a soft brush, then apply diluted PVA glue (50:50 with water plus a drop of washing-up liquid) using a dropper or pipette. Let it dry for 24 hours before running trains.

ModelCalcs.uk

Ballast Calculator — Model Railway

Calculate ballast volume and weight needed for model railway track sections.

Track Length

Total running length of plain track to ballast (add up all sections; count points separately below)

GaugeSets the ballast bed width and depth used for the bed profile (e.g. OO ≈ 30mm wide × 3mm deep)

Track TypeSingle or double track mainline

Points / Turnouts

Number of points that need ballasting

Ballast Bag Cost

Cost per bag of ballast

How We Calculate This

Calculation

Cross-section area = Ballast width x Depth x 0.7 (trapezoidal profile)

Volume = Total track length x Cross-section area

Weight = Volume × Ballast density (1.5 g/cm³, the loose bulk density of fine crushed-granite ballast, which sits in the 1.4-1.6 g/cm³ range)

PVA glue ≈ equal volume to the ballast — roughly 50ml of diluted glue per 100g of ballast. Mix 50:50 PVA and water with a drop of washing-up liquid, then flood it on with a pipette until the ballast is soaked.

Points are treated as extra track length based on gauge (an OO point adds about 170mm). The trapezoidal factor (0.7) accounts for the sloped shoulder profile of realistic ballast — the bed is a thin shouldered layer, not a solid block. Buy a little extra to allow for spillage and sweeping off the excess.

Frequently Asked Questions

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Last updated: March 2026

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