ISO/IEC 17025 explained: requirements, accreditation and how to check a calibration lab

ISO/IEC 17025 is the international standard for the competence of testing and calibration laboratories. Its full title is General requirements for the competence of testing and calibration laboratories, and the current edition is ISO/IEC 17025:2017. ISO reviewed and confirmed it in 2023, and as of October 2026 no revision is under way. Labs are accredited to it, not certified: an accreditation body (in the US, A2LA, ANAB, IAS, NAC, NVLAP or PJLA) assesses the lab’s technical competence for a defined scope of calibrations. Since January 1, 2026, international recognition of that accreditation runs through Global ACI, which replaced ILAC and IAF. This page covers both sides of the counter: what accreditation guarantees when you buy calibration, and what it takes to get accredited.

A note on sources: ISO/IEC 17025 is a paid standard and we do not reproduce its text. We describe requirements in our own words, cite only clause numbers, and base the descriptions on free documents from accreditation bodies (A2LA, ANAB, NVLAP, PJLA, NATA), Global ACI and NIST, listed at the end. Where only one secondary source supports a detail, we say so.

What ISO/IEC 17025 is, and which edition is current

ISO/IEC 17025 is a joint ISO and IEC standard, developed under ISO’s committee for conformity assessment, ISO/CASCO (ISO catalog; ISO, 2017). It is meant for every kind of lab, large or small, that tests, calibrates, or samples for later testing or calibration (ANAB; ISO catalog). Customers and regulators rely on it to judge whether a lab is competent, and accreditation bodies assess labs against it (ANAB; ISO catalog).

The 2017 edition brought four main changes, according to ISO: a scope that covers sampling linked to later testing or calibration; a process approach aligned with newer standards such as ISO 9001; more attention to information technology, including computer systems and electronic records and reports; and a new emphasis on risk-based thinking (ISO, 2017). If you are choosing a system to hold calibration data and records, our calibration management software guide covers what to check. Accredited labs had three years to move to it, until late 2020 (ISO, 2017).

Is a new version coming? Not that anyone has announced. ISO reviews every standard every five years, and the last review ended in confirmation in 2023 (ISO catalog). As of October 9, 2026, ISO/CASCO’s list of projects under development contains no ISO/IEC 17025 project, and Global ACI’s list of normative documents shows ISO/IEC 17025:2017 with no transition (ISO/CASCO catalog; Global ACI-FMRA-001). Talk of a “2026 version” may come from a sister standard that did get a new edition in 2026: ISO/IEC 17020, for inspection bodies, whose transition ends on March 27, 2029 (Global ACI-FMRA-001).

Accreditation, not certification

Accreditation is an independent evaluation of a body such as a lab against recognized standards, to confirm its impartiality and its competence to carry out specific activities, such as particular calibrations (Global ACI FAQ; A2LA, 10 Steps). Certification of a management system, as with ISO 9001, attests that the system meets requirements; it is not a statement of technical competence (A2LA, 10 Steps). That is why labs are accredited to ISO/IEC 17025. “ISO 17025 certification” is a common search and a common marketing phrase, and it usually means accreditation.

Two more distinctions that cause confusion:

• Who checks the checkers. Accreditation bodies are themselves evaluated by their peers against ISO/IEC 17011; labs are assessed against ISO/IEC 17025 (Global ACI; NIST HB 150). An accreditation body may not act as a consultant to the labs it accredits, though it can offer an optional preliminary assessment (ANAB MA 2100; PJLA, 5 Steps).
• NIST is not an accreditation standard. NIST is the US national metrology institute. It does not certify the traceability of results it did not produce (NIST traceability FAQ). NVLAP, a program run by NIST, is one of the US accreditation bodies (Global ACI signatory list). “NIST-certified lab” is not a thing; “NVLAP-accredited lab” is.

The structure of the standard: clauses 4 to 8

ISO/IEC 17025:2017 has eight clauses. Clauses 1 to 3 cover scope, normative references, and terms and definitions; the requirements sit in clauses 4 to 8 (A2LA, 10 Steps; NIST HB 150-2). The table gives the sub-clause titles in paraphrase and what each block means in a calibration lab.

Sub-clause numbers in clauses 4, 6 and 7 are confirmed by NIST HB 150-2 and other accreditation-body documents. For clause 8, the numbers of 8.1, 8.3, 8.4, 8.6, 8.8 and 8.9 are confirmed; the others carry medium confidence, so we list them by topic only.

Option A or B (clause 8.1). Under option A, the lab implements the management system requirements of clause 8 itself. Under option B, the lab runs a management system built to ISO 9001 that lets it meet clauses 4 to 7 consistently. NATA, the Australian accreditation body, explains that with option B and an ISO 9001 certificate from an accredited certification body, the accreditation body may not need to assess the whole management system (NATA, Standard Application Document, 8.1).

Results, not recipes. Most requirements say what must be achieved, not how. Clause 6.3, for example, asks the lab to document the environmental conditions that affect its results and to monitor and record them; it does not set temperature or humidity limits (PJLA, Sections 6.3 & 6.4). NVLAP, for example, puts its field-specific environmental requirements in its own handbook, not in the standard (NIST HB 150-2, 6.3). That is why two accredited labs can look very different, and why the scope and the uncertainty matter more than the logo.

For a clause-by-clause walk-through, see our guide to ISO/IEC 17025 requirements.

What accreditation guarantees when you buy calibration

If you send instruments to an accredited lab, these are the requirements that protect you, and what you should see as a result:

Some things accreditation does not guarantee:

• Work outside the scope. Accredited labs also do non-accredited work. Only results within the scope can carry the accreditation symbol, and other results must be identified (A2LA R105, §1.7.4; Global ACI-MRA-006, §9.8, formerly ILAC P8).
• Every individual result. The symbol means the lab is accredited for that work, not that the accreditation body checked your results (A2LA R105, §1.7.2–1.7.3; NIST HB 150, Annex A).
• Fitness for your process. The lab usually checks the manufacturer’s specification. Whether the instrument is good enough for your tolerance, and when to calibrate it again, is your decision.
• That you get the CMC. The CMC is the lab’s best case. The uncertainty for your instrument is normally larger (Global ACI-TECH-1-009, §5.4).

How accreditation reaches your certificate (Global ACI in 2026)

Accreditation is a chain of trust. Each level is assessed by the one above, and at each level there is something you can check in a few minutes:

What changed on January 1, 2026. IAF and ILAC merged into a single organization, Global Accreditation Cooperation Incorporated (Global ACI), which took over all their activities. Since that date, international recognition runs through the Global ACI MRA; the ILAC MRA no longer operates as a separate arrangement (Global ACI; Global ACI FAQ). For US calibration customers, nothing broke: the US accreditation bodies remain signatories for calibration, with their original admission dates (Global ACI signatory list, September 25, 2026). The list has six US signatories for calibration:

The ILAC MRA mark is still legitimate during the transition. Accreditation bodies authorized to use the ILAC MRA mark at the end of 2025 may keep using it until the Global ACI MRA mark is legally available in their economy. From then on, new, renewed or amended documents carry the new mark, and older documents can remain valid (Global ACI FAQ). Using the MRA mark is optional in any case: an accredited certificate can carry only the accreditation body’s symbol (Global ACI, MRA Mark; ILAC P10).

Renamed documents. Many ILAC documents you see cited on certificates and in audits now have Global ACI numbers (Global ACI cross-reference table, v14.0):

Some accreditation-body documents still cite the old ILAC numbers (ANAB AR 2251, for example, still refers to P14); others already use the new ones (A2LA G118). Both point to the same requirements.

How to read a lab’s scope and CMC

The scope of accreditation is the accreditation body’s published list of exactly which calibrations a lab is accredited for. It tells you what the accreditation covers, since the lab may do other, non-accredited work (A2LA G118, §I; ANAB MA 2100). Scopes are public: US accreditation bodies publish them in their online directories (ANAB MA 2100; PJLA, 5 Steps). Global ACI advises purchasers to check with the lab, confirm that its accreditation body is on Global ACI’s list of recognized signatories, and use that body’s online directory (Global ACI FAQ). The one-page accreditation certificate on a lab’s website is not enough; the scope is the attachment that matters.

A calibration scope is a table, grouped by discipline (dimensional, electrical, mechanical, thermodynamic and so on), with four columns (A2LA G118, §III):

How to read it:

• CMC stands for calibration and measurement capability: the best uncertainty the lab can deliver under its accreditation, for a normal calibration of a close-to-perfect instrument. It is an expanded uncertainty at about 95 %, usually with k = 2 (A2LA G118, example notes; Global ACI-TECH-1-009, §4.3).
• Your uncertainty will be larger. Your instrument’s resolution, repeatability and other contributions add to the CMC. In the example above, the CMC at 300 psi is 0.012 % × 300 + 0.02 = 0.056 psi. Our example certificate for a 300 psi gauge reports U = 0.12 psi: larger, as expected. A certificate with U smaller than the CMC is a red flag: accredited labs may not report it (Global ACI-TECH-1-009, §5.4–5.5).
• On-site calibration usually has a larger uncertainty than the CMC, because of the environment, transport and the instrument itself (A2LA G118, example notes).
• A CMC applies across its whole range, which is why scopes split ranges into rows (A2LA G118, §III).

Then compare with your need. If your tolerance is ±0.75 psi and the lab can deliver U = 0.12 psi, the test uncertainty ratio is 1.50 / 0.24 ≈ 6.2:1. The TUR calculator does this and shows the false-accept risk. A ratio of 4:1 is a common industry convention, not an ISO/IEC 17025 requirement (A2LA G136).

To search accredited labs by parameter, use the accreditation bodies’ directories or our directory of accredited calibration labs.

Checklist: how to vet an accredited calibration lab

Use this before you add a calibration supplier, and again when a supplier’s accreditation is renewed or its scope changes.

ISO/IEC 17025 vs ISO 9001

The two standards are often confused because a lab can hold both, and because ISO 9001 users buy calibration from 17025 labs.

Two points that often get lost: meeting ISO/IEC 17025 does not mean a lab holds an ISO 9001 certificate, and holding ISO 9001 says nothing about a lab’s measurement capability. For what ISO 9001 asks of your own instruments, see ISO 9001 calibration requirements (clause 7.1.5). For automotive suppliers, IATF 16949 does require external labs accredited to ISO/IEC 17025, or equivalent evidence (IATF SI 10). ISO 10012 is a third, separate standard for measurement management systems.

Getting accredited: where calibration labs spend the effort

For a lab considering accreditation, most of the work is technical, and it is concentrated in a few places. These are the areas the requirements and the accreditation bodies’ own policies put most weight on:

1. An uncertainty budget for every line of the scope. Clause 7.6 requires an uncertainty evaluation for all calibrations, and ANAB asks for an expanded uncertainty at about 95 % for each line of the scope (ANAB AR 2251; Global ACI-TECH-1-009). Your CMCs come out of these budgets. Our uncertainty calculator and uncertainty guide walk through one.
2. Traceability of your own reference standards. Every standard must trace to the SI through accredited labs or national metrology institutes, under the accreditation body’s traceability policy (clause 6.5; ILAC P10; A2LA P102). Check the certificate of each reference standard against that policy early, before the assessor does.
3. Proficiency testing. You need a plan for proficiency tests or interlaboratory comparisons that covers your scope over time (clause 7.7; PJLA, 5 Steps). For some parameters, finding a provider is the hard part.
4. Decision rules. If you issue pass/fail statements, you need a documented rule that accounts for uncertainty and is agreed with customers (clauses 3.7, 7.1.3, 7.8.6; Global ACI-TECH-1-002). See guard banding.
5. A realistic scope. Each row of the scope needs a method, equipment, a budget and evidence. You can start with a narrow scope; accreditation bodies allow scope extensions later, sometimes with a document review only (PJLA, 5 Steps; ANAB MA 2100). A2LA G118 explains how to write a calibration scope.
6. Internal audit and management review before you apply. A2LA lists both as steps before the assessment (clauses 8.8 and 8.9), and ANAB expects them to cover all elements within the 12 months before the initial assessment (A2LA, 10 Steps; ANAB MA 2100). A2LA adds that the standard does not prescribe specific training for internal auditors (A2LA, 10 Steps).
7. The accreditation body’s own policies. You are assessed against ISO/IEC 17025 and the body’s requirements on traceability, uncertainty, proficiency testing, scope and use of the symbol: for example ANAB AR 2251, A2LA P102 and R105, PJLA’s policies, or NIST HB 150 and 150-2 for NVLAP (PJLA, 5 Steps; ANAB MA 2100). Some programs add sector requirements on top, such as automotive, aerospace or FDA programs at ANAB (ANAB).

The accreditation process with US accreditation bodies

The steps are broadly the same at A2LA, ANAB, NVLAP and PJLA. This sequence combines A2LA’s ten steps, ANAB’s accreditation manual and PJLA’s five-step process:

1. 1

   Get the standard and your body's requirements

   Buy ISO/IEC 17025:2017 and read the accreditation body's policies, which you will be assessed against as well (A2LA, 10 Steps; PJLA, 5 Steps).

2. 2

   Define the scope you will apply for

   Parameters, ranges, methods and CMCs backed by uncertainty budgets (A2LA G118).

3. 3

   Document and implement

   Management system and technical procedures, in use and producing records. A2LA notes that documentation alone can take several months.

4. 4

   Internal audit and management review

   Covering all elements, before applying; ANAB expects both within the 12 months before the initial assessment (ANAB MA 2100).

5. 5

   Apply and get a quote

   The quote depends on the scope, locations, staff and on-site work. PJLA quotes a full two-year cycle (ANAB MA 2100; PJLA, 5 Steps). An optional preliminary assessment is available at some bodies.

6. 6

   Document review and on-site assessment

   PJLA asks for documents 30 days before the visit; assessors review the system and witness calibrations being performed (PJLA, 5 Steps).

7. 7

   Close the findings

   Corrective actions within 60 days at PJLA; responses to nonconformities within 30 days at NVLAP (PJLA, 5 Steps; NIST HB 150, §3.3.4.1).

   Findings open: no decision yet

8. 8

   Accreditation decision

   Made by people independent of the assessor. The certificate and scope are published in the body's directory (PJLA, 5 Steps; ANAB MA 2100).

9. 9

   Surveillance and reassessment

   A two-year cycle with assessment activity every year (ANAB MA 2100; PJLA, 5 Steps). NVLAP assesses on site before initial accreditation, during the first year and every two years after (NIST HB 150, §3.2.3.3, §3.6.1).

Cost. Only one US accreditation body publishes its fees. At the time of writing, NVLAP charges a $1,000 non-refundable initial application fee, a $5,750 yearly administrative and technical fee, plus on-site assessment costs (variable for calibration, quoted per lab) and proficiency testing, which is paid separately (NVLAP Fee Structure, updated July 27, 2026). A2LA, ANAB and PJLA give individual quotes (ANAB MA 2100; PJLA, 5 Steps). On top of that come your own costs: the standard, staff time, calibration of your reference standards and proficiency tests. We have found no reliable published figure for a typical total, and we do not quote the numbers that circulate on forums.

Time. No US accreditation body publishes a typical timeline. The fixed deadlines are the partial ones listed in the steps above. The “30/60/90 days” or “six months of records” rules you may hear from consultants are not in any accreditation body document we found.

Where to get ISO/IEC 17025 (and the “free PDF”)

ISO/IEC 17025:2017 is sold by ISO, CHF 179 at the time of writing, as PDF or ePub, with a “redline” version also available (ISO catalog), and by national standards bodies. Copies offered as “free download” are unauthorized.

Free, official documents that explain much of what it means in practice:

• NIST Handbook 150 and 150-2 (NVLAP procedures and calibration-lab requirements), public domain.
• Accreditation-body guidance, such as A2LA G118 (calibration scopes), A2LA G136 (decision rules) and ANAB AR 2251 (requirements for calibration labs).
• Global ACI policies, such as TECH-1-009 (uncertainty in calibration) and TECH-1-002 (decision rules), and ILAC P10 (traceability).
• NIST’s 17025 crosswalks, such as the one for clause 7.8 on reporting results.

From here, the practical guides: how to review a calibration certificate, how to set up a calibration program, and measurement uncertainty explained.