How to determine a calibration interval

• Calibration
• Updated: 4 October 2026
• About 4 min read

Steps for setting the interval

1. 1

   Choose the initial interval

   A new instrument has no history, so the initial interval is chosen by considering the manufacturer's recommendation, experience with similar instruments, the frequency of use and how critical the measurement is. Many organisations start with one year; this is not a rule, only a common starting point.

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2. 2

   Monitor past results

   Record the instrument's deviation at every calibration and follow it over time. If the deviation stays well inside the tolerance each time, the interval can be extended; if it approaches or exceeds the tolerance limit, the interval should be shortened. Intermediate checks carried out between calibrations (e.g. a quick verification against a check standard) also provide data for this decision.

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3. 3

   Weigh up the factors and record the decision

   The following factors are considered together when deciding the interval: frequency and severity of use, the working environment (temperature, vibration, dust), whether the instrument has suffered a knock, the effect of the measurement on product quality or safety, the age and repair history of the instrument, and regulatory or customer requirements. Record your decision and the reasons for it; it is one of the first things an auditor will ask about.

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The methods in ILAC-G24 (an overview)

ILAC-G24 / OIML D 10, a guideline published jointly by ILAC and OIML, proposes methods for determining and reviewing calibration intervals. Roughly summarised, these are:

• The staircase (automatic adjustment) approach: If the instrument is found within tolerance at a calibration the interval is extended; if it is outside, the interval is shortened.
• Control chart: The results at selected calibration points are plotted on a chart and the interval is adjusted according to the drift trend.
• In-use time: The instrument is calibrated according to the hours it has been in operation rather than the calendar.
• The in-service check ("black box") approach: The instrument is given a simple check at regular intervals and is sent for a full calibration if a problem is found.

Which method is suitable depends on the number of instruments, the data available and the level of risk; refer to the guideline itself for the details.

Record keeping

For each instrument, keep the calibration dates, the results, the deviations, the intermediate check results, the repairs and the reasons for any change of interval in the same place. These records let you base the interval on data and also demonstrate your decisions at an audit. For the tracking list, see the guide How to keep an equipment calibration tracking list.

Frequently asked questions

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