Weighbridge

A weighbridge is a scale big enough to weigh a whole road vehicle, loaded or empty, to find the weight of what it carries. When that weight sets a price, toll or tax, the scale must meet legal metrology rules — NIST Handbook 44 in the US, the non-automatic weighing instruments directive in the EU.

What it is used for

• Trade: goods sold by weight are priced on the net — the loaded weight less the empty vehicle.
• Containers: method 1 of SOLAS VGM is weighing the packed container, by the shipper or a third party it arranges.
• Road limits: in the US, 80,000 lb gross, 20,000 lb on a single axle and 34,000 lb on a tandem; in the EU, 40 t, or 44 t for an intermodal container load.
• Gate records: the weight is captured with the gate pass at a port or plant.

Legal for trade

NIST Handbook 44 defines a vehicle scale as one adapted to weighing highway, farm or other large industrial vehicles, and sets its tolerances by accuracy class, typically III L. The EU directive covers instruments that need an operator during weighing, used for commercial transactions or to set a toll, tariff or tax. In the UK, it is illegal to operate a chargeable weighbridge without a certificate of competence; records are kept for 2 years, and an offence can bring a fine of up to £5,000 and 6 months in prison. India's July 2026 legal metrology amendment requires test weights of half the scale's capacity, reducible to a third or a fifth when the scale's repeatability is good enough.

Worked example: how much error is allowed

The mistake people make

Treating an enforcement tolerance as an allowance. The UK's Maritime and Coastguard Agency checks container VGMs to ±5% or ±500 kg, whichever is greater, but says that figure is for enforcers' guidance only — it is the shipper's responsibility to be accurate.