Weighbridge calibration in India — what to expect, what it costs

A practical guide for weighbridge owners and yard supervisors

A weighbridge is a legal-trade instrument. Until it has been calibrated by a recognised surveyor and stamped by the Legal Metrology Department, you cannot use it for commercial weighing. Stamping is mandatory under the Legal Metrology Act 2009 and re-stamping is mandatory annually thereafter. The actual on-site work — bringing standard weights, running corner-load and span tests, sealing the indicator — is invisible to most yard owners until the bill arrives. This article walks through what happens, why, what it costs, and what trips it up.

Why a weighbridge has to be re-calibrated

Three independent drifts push every weighbridge out of true over time:

• Mechanical settling. The deck moves microscopically over months of heavy trucks. Bolts loosen, ribs flex, the cell-load distribution shifts. After 8–12 months the corner loads no longer sum cleanly.
• Cell aging. Strain gauges drift slowly. A 2 mV/V cell may read 2.005 mV/V after a year. The drift is small but cumulative across 6 or 8 cells.
• Environmental damage. Monsoon water intrusion, lightning strikes, rodent-chewed cables, dust in the junction box. None of these fail catastrophically — they shift the readings by a kilogram or two.

Re-calibration corrects all three together. The surveyor places known weights on the deck, the indicator is told "this should read X kg," and the firmware adjusts its span and zero offsets. New seals get fitted, a new stamping date is printed, and the weighbridge is legally usable for another year.

Legal Metrology stamping vs. calibration

These two terms are often used interchangeably but are different events. Both happen at the same site visit, but the responsibilities differ:

The surveyor calibrates and certifies. The inspector verifies and stamps. In practice both attend the same site visit, often on the same day, but the surveyor's certificate is what your vendor + cell warranty are tied to, while the inspector's stamp is what the regulator checks.

The annual cycle, from first-fit to next year

From the day a new weighbridge is commissioned, here is the calibration cycle most Indian yards follow:

Who does what — owner, vendor, surveyor, inspector

• Owner (you): schedules the visit, arranges site access for the standard-weight truck, pays the vendor + surveyor + inspector fees.
• Vendor (Eagle Weigh in our case): coordinates with the surveyor + inspector, runs the indicator-side adjustments, applies the new seal and date label to the indicator. The vendor is your point of contact for the whole event.
• Surveyor: a Govt-recognised individual or firm with access to standard test weights. Brings the weights on a truck, runs the technical calibration, signs the certificate.
• Legal Metrology Inspector: a state Govt employee who attends, verifies the surveyor's result, applies the tamper-evident metal seal on the indicator, and updates the central register. Gets a small statutory fee.

If you have an active vendor support contract — Eagle's annual support, for example — the vendor coordinates the surveyor and inspector visit for you. Owners running without support typically have to call each party separately, which is the #1 reason calibrations get delayed past the 12-month mark.

How the on-site calibration actually runs

A full re-calibration takes 4–6 hours of on-site work for a 60-tonne weighbridge. Here is what happens, step by step.

The weights — where they come from

The surveyor arrives with standard test weights — cylindrical or rectangular cast-iron blocks of known mass, certified and stamped by NPL (National Physical Laboratory) or an NPL-traceable lab. A typical kit for a 60 t weighbridge: 20–25 weights of 1 t each, plus a few smaller weights of 500 kg, 100 kg and 20 kg for span verification. The weights themselves arrive on a flatbed truck.

Corner-load test

The first test. The surveyor places a known weight (typically 5 t or 10 t) sequentially on each cell corner of the deck — first the front-left cell, then front-right, then rear-left, then rear-right. Each reading is recorded. The four readings should match within a tight tolerance (under 0.03% of full scale). If one corner reads differently, the cell at that corner is faulty or the load-distribution has shifted.

Eccentric-load + repeatability

The same weight is then placed at half-deck position (centre of one half), then quarter-positions. The readings should be consistent — within the same tolerance band. The same weight is also placed three times at the same position; the three readings should be within 1 division of each other.

Span calibration

The bulk of the visit. Standard weights are loaded onto the deck in steps — 10 t, 20 t, 30 t, 40 t, 50 t, 60 t, then the same load points coming back down. At each load step, the indicator reading is compared to the known weight. If the readings drift, the surveyor adjusts the indicator's span calibration value until each step reads correctly within tolerance. The whole sequence is run twice.

What tolerances apply

For a Class III weighbridge under OIML R76 (which is what Indian Legal Metrology requires), the maximum permissible error is ±0.05% of the maximum capacity for verification. On a 60 t weighbridge that is ±30 kg at full scale. Most weighbridges in good condition calibrate within ±15 kg — well inside tolerance.

What it costs in 2026

Realistic 2026 total for an annual re-calibration of a 60-tonne weighbridge: ₹30,000 – 50,000. Larger weighbridges, remote sites, and out-of-cycle retests all push this higher.

When you need an unscheduled retest

Five common triggers for an out-of-cycle calibration + re-stamping:

1. Indicator replaced or repaired. Even if the cells are fine, the indicator change requires re-calibration because the new indicator has to learn the cells' actual sensitivity values.
2. Cell replaced. Same logic — the new cell's mV/V is not identical to the old one's. Always replace cells in matched sets if possible; single-cell replacement always needs re-calibration.
3. Deck mechanical work. Any welding, bolt-tightening, rib-replacement, or under-deck levelling.
4. Customer dispute or weighment challenge. If a trucker disputes a weighment in court or with a Legal Metrology complaint, the inspector orders a verification weigh-in. If the result is outside tolerance, full re-calibration is mandatory.
5. Seal broken. Tamper-evident seals on the indicator and junction box are not allowed to be broken outside of calibration. A broken seal — including from rodent damage or vendor work — voids the stamping and requires a fresh inspection.

Five reasons calibrations fail

1. Surveyor cannot get to the site on the scheduled day. Weather, mining-area access restrictions, or surveyor's own scheduling. Always book 4–6 weeks ahead of the expiry date.
2. Standard-weight truck cannot reach the deck. Some mining sites have ramp restrictions or yard layouts that block the weight-truck. Inspect access before booking.
3. Corner-load test fails. Indicates a faulty cell. The calibration is paused, the cell is replaced, and the visit re-scheduled. Adds 2–3 weeks.
4. Inspector unavailable. The Legal Metrology inspector is a state employee with a heavy schedule. If they cannot attend on the surveyor's day, the calibration certificate is held without stamping until the inspector arrives.
5. Indicator firmware too old to accept new span values. Rare but happens with very old indicators. The fix is an indicator upgrade — at which point you have a chance to upgrade other things too.

If you run a weighbridge fleet — multiple yards under one operator — coordinating calibrations is its own project. Eagle's annual support bundles the surveyor + inspector coordination for every yard on the contract; we send a single calendar of dates and you only need to ensure site access.

Learn more about the indicator + terminal options we manufacture and the EagleOS software that records calibration dates as part of every printed slip.

Last updated: June 2026 · Eagle Weigh editorial team