What is a weighbridge? A working guide for UK farms

A weighbridge is a large set of scales built into or onto the ground, big enough to weigh a whole vehicle at once. You drive a loaded trailer on, take a reading, tip, then weigh the empty vehicle on the way out. The difference between the two readings is the weight of the load. On an arable farm that number is the backbone of everything: what came off each field, what went into each shed, and what left on a lorry.

This guide covers how weighbridges work, what they cost to use or install, the rules around using one "for trade", and the alternatives if a full bridge doesn't stack up for your acreage.

How a weighbridge works

Most weighbridges are a steel or concrete deck sitting on load cells — sensors that convert the force pressing down on them into an electrical signal. An indicator in the office or on a post by the deck turns that signal into a reading, usually to the nearest 20kg on a 50-tonne bridge.

There are two ways to get a load weight:

• Gross and tare. Weigh the loaded vehicle (gross), tip, weigh it empty (tare). Load weight = gross minus tare. This is the standard method during harvest because trailer weights change — wet mud on a chassis after a catchy week can add a surprising amount.
• Stored tare. Weigh each trailer empty once, store the figure, and only weigh loaded vehicles from then on. Quicker, but the stored tare drifts as conditions change, so most farms re-tare at least daily in a wet harvest.

A full-length bridge weighs the whole vehicle in one pass. Shorter decks and axle pads weigh one axle at a time and add the results — cheaper, but slower and less accurate, and not normally certifiable for trade.

What does it cost to use a public weighbridge?

If you don't have your own bridge, public weighbridges typically charge somewhere between £10 and £15 plus VAT per weighing, with some as low as £5 and busy sites nearer £20. A gross-and-tare pair counts as two weighings at most sites, so budget £20–£30 to get one certified load weight.

You can find your nearest one through the gov.uk find-a-weighbridge service, which points you at your local council's register. Ring before you go: opening hours are usually working hours only, some sites want cash or an account, and not every bridge takes an artic or a tractor with a 24-foot trailer.

For the odd load — checking a lorry isn't overloaded before it goes on the road, or settling a dispute with a merchant — paying per weighing is fine. If you're moving a few thousand tonnes a year through someone else's bridge, the maths starts pointing at your own.

What does a farm weighbridge cost to buy?

As a rough guide for the UK:

Option	Typical installed cost	Notes
New 50t full-length bridge (steel deck, surface mounted)	£25,000–£45,000	The standard option. Surface-mounted avoids digging a pit but needs ramps.
New pit-mounted bridge	£35,000–£60,000	Flush with the yard, easier to sweep, dearer groundworks.
Refurbished / second-hand bridge	£12,000–£25,000	Worth it if the load cells and deck are sound. Get it inspected.
Axle weigh pads	£3,000–£8,000	Portable, fine for overload checks. Not trade-approved as a rule.

On top of that, allow for groundworks (a level concrete approach either end matters more than people think), power to the indicator, and an annual service. Load cells drift; a calibration check once a year keeps the numbers honest and is required if the bridge is certified for trade.

The payback question is simple enough: at £25 per public weighing pair, a bridge that costs £30,000 breaks even somewhere around 1,200 weighed loads — but that misses the real value, which is that you weigh every load when the bridge is in the yard, not just the ones worth a trip. That's what turns weighing from an occasional check into actual harvest data: tonnes per field, shed fill, and a running total you can sell against.

Certification: when "for trade" matters

Under the Weights and Measures Act 1985, a weighbridge must be approved and verified if the weights are used "for trade" — meaning the reading determines what somebody pays. Selling grain over your own bridge on your own figures is use for trade; the bridge needs to be a stamped, verified installation, and Trading Standards can inspect it.

If your bridge is only used for your own management — field yields, shed stock, drier throughput — certification isn't required, though plenty of farms keep an uncertified bridge honest with an annual calibration anyway. When grain is sold, the buyer's certified weighbridge (or the mill's intake bridge) provides the trade weight.

Public weighbridge operators also need a certificate of competence from their local Weights and Measures authority — which is why the person in the kiosk takes the ticket seriously.

Do you actually need one?

A rough rule of thumb by tonnage:

• Under ~1,000t a year: probably not. Use the merchant's intake weights, hire in for the odd check, and keep good load records so you spot discrepancies.
• 1,000–3,000t: borderline. A second-hand bridge or a shared bridge with a neighbour often makes sense, especially if you store grain and sell in batches through the year.
• Over ~3,000t, or storing for others: yes. You want your own numbers at intake, not just the mill's numbers at outturn — the difference between the two is where shrinkage, drying loss, and disputes live.

Whatever you weigh on, the reading is only worth anything if it's written down against the right field, crop, and shed. A bridge with no record-keeping behind it is an expensive way to satisfy curiosity — see our guide to weighbridge tickets for what to capture on every load.

Frequently Asked Questions

What is a weighbridge in simple terms?

A weighbridge is a vehicle-sized set of scales set into or onto the ground. You weigh a vehicle loaded, weigh it empty, and the difference is the weight of the load. Farms use them to measure grain coming off fields and going in and out of stores.

How much does it cost to use a public weighbridge in the UK?

Typically £10–£15 plus VAT per weighing, with some sites cheaper and some nearer £20. Getting a load weight needs two weighings (loaded and empty), so budget £20–£30 per load. Ring ahead to check hours, payment, and whether your vehicle fits.

How much does a farm weighbridge cost to install?

A new 50-tonne surface-mounted weighbridge typically costs £25,000–£45,000 installed. Pit-mounted bridges cost more because of groundworks, and sound refurbished bridges can be had from around £12,000. Budget for a concrete approach and an annual calibration on top.

Does a farm weighbridge need to be certified?

Only if the weights are used for trade — that is, if somebody pays based on the reading. Selling grain on your own bridge's figures requires an approved, verified installation. Weighing purely for your own records doesn't, though an annual calibration is still sensible.

How accurate is a weighbridge?

A well-maintained 50-tonne bridge typically reads to the nearest 20kg, which is better than 0.1% on a full grain trailer. Accuracy depends on level approaches, clean load cells, and regular calibration — a neglected bridge drifts.