How to Write a Lab SOP: Template & Guide

A Standard Operating Procedure (SOP) is the written document that turns a lab technique into something repeatable, trainable, and defensible — the same test run the same way regardless of who is at the bench. This guide is about the mechanics of producing one: what sections a working lab SOP actually needs, how to draft the procedure steps themselves, how to get it reviewed and validated before anyone relies on it, and how to keep it current once it’s in use. For the underlying concept and how an SOP differs from a protocol, policy, or work instruction, see CASRAI’s Standard Operating Procedure (SOP) dictionary entry; this guide picks up where that definition leaves off.

Most searches for this topic actually land on the phrase ‘SOP template’ rather than the literal question ‘how do I write one’ — so if you came here looking for a ready structure to adapt, skip to the template section below. The rest of the guide walks through why that structure exists and how to fill it in well.

Why a Lab Needs Written SOPs, Not Just Institutional Knowledge

An unwritten procedure that lives only in one person’s head is a single point of failure: it doesn’t survive staff turnover, it can’t be audited, and it produces silent drift as each person who learns it ‘by watching’ introduces small variations. Written SOPs solve three distinct problems at once:

Reproducibility. If two technicians run the same assay a year apart and get different results, an SOP is the first place to check for undocumented variation in reagent prep, timing, or equipment settings.
Training and onboarding. A new lab member can be trained against a document, checked off against it, and held to the same standard as everyone else — rather than trained purely by informal apprenticeship.
Regulatory and funder compliance. Several frameworks make written SOPs an explicit requirement, not just a best practice. Under the FDA’s Good Laboratory Practice regulations (21 CFR 58.81), nonclinical safety-testing facilities must have written SOPs covering the study-relevant procedures actually performed there, and any deviation from an approved SOP has to be authorized and documented by the study director — see CASRAI’s Good Laboratory Practice (GLP) entry for how this fits into the broader GLP framework. ISO/IEC 17025, the general standard for the competence of testing and calibration laboratories, likewise requires documented procedures for the methods a lab performs. Institutional biosafety committees, IACUCs, and radiation safety committees commonly require an approved SOP as a condition of protocol approval, independent of any product-testing regulation.

None of this requires a large or formal lab. A two-person academic bench running the same PCR assay every week benefits from a written SOP just as much as a regulated testing facility does — the difference is only how formal the review and approval process needs to be.

SOP, Protocol, or Work Instruction: Choosing the Right Document Type

These terms get used loosely and interchangeably in practice, but it’s worth being deliberate about which one you’re actually writing:

SOP — a general, institution- or lab-level procedure for a recurring activity (e.g., ‘Autoclave Operation and Maintenance,’ ‘Chemical Waste Labeling’). Written once, used repeatedly, revised on a schedule.
Protocol — often study- or experiment-specific, sometimes citing one or more SOPs by reference rather than repeating their content (e.g., a grant-funded study’s methods section cites ‘per SOP-014, RNA Extraction’).
Work instruction — a narrower, more granular document than an SOP, sometimes used for a single step within a larger SOP (e.g., ‘How to Program the Thermocycler’), particularly in ISO 9001-aligned quality systems that distinguish tiers of documentation.

For most academic and core-facility labs, this distinction doesn’t need to be rigid — a single-tier SOP library covering both the general procedure and the equipment-specific detail is common and perfectly workable. Regulated environments (GLP facilities, clinical labs, ISO-accredited testing labs) are more likely to maintain the tiered structure formally.

The Standard Anatomy of a Lab SOP

Regardless of format, a working lab SOP almost always contains the same functional sections. Missing any of these is the most common reason an SOP fails an audit or fails to actually get followed:

Header/identification block — SOP title, unique ID number, version number, effective date, author, and approver. This is what makes the document controllable: without a version number, there’s no way to know which copy someone is following.
Purpose and scope — one or two sentences on what the procedure accomplishes and, just as importantly, what it does not cover (e.g., ‘this SOP covers routine calibration; for repair after a failed calibration, see SOP-022’).
Responsibilities — who is authorized to perform the procedure, and who is responsible for maintaining the SOP itself.
Safety and hazard information — required PPE, specific hazards (chemical, biological, physical), and any engineering controls (fume hood, biosafety cabinet) the procedure depends on. This section is frequently the difference between a document EHS will sign off on and one they won’t.
Materials, reagents, and equipment — a complete list, including model/catalog specificity where it matters (a step that says ‘centrifuge the sample’ is not the same instruction on a benchtop microcentrifuge as on a floor-model ultracentrifuge).
Procedure — the actual numbered steps. See the next section for how to write these well.
Quality control / acceptance criteria — how the person running the procedure knows it worked (expected values, controls that must pass, acceptable ranges) versus when to stop and troubleshoot.
Troubleshooting — the two or three failure modes that come up often enough to be worth documenting, and what to check first.
References — the source method, published protocol, manufacturer manual, or regulation the SOP is based on.
Revision history and approval signatures — who approved this version, when, and what changed from the previous one.

How to Write the Procedure Steps Themselves

The header and boilerplate sections above are largely fill-in-the-blank. The procedure section is where SOPs succeed or fail, because it’s the part someone actually follows at the bench under time pressure. A few concrete practices make a meaningful difference:

Write it while doing it, not from memory afterward. Draft the numbered steps by actually performing the procedure and writing down each action as you take it, including things an expert might consider too obvious to mention (which temperature, which tube type, which setting). What’s obvious to the person who’s done a procedure five hundred times is frequently the exact detail a new trainee needs and doesn’t have.
One action per numbered step. ‘Add 500 µL of buffer and vortex for 10 seconds’ is really two actions; splitting it makes the step easier to follow and easier to reference when troubleshooting (‘did you complete step 4b?’).
Use specific, checkable values, not qualitative ones. ‘Incubate until the solution turns clear’ is harder to follow consistently than ‘incubate at 37°C for 15–20 minutes.’ Where a range is genuinely acceptable, state the range rather than forcing a single value that isn’t actually critical.
Separate the critical steps from the flexible ones. If a specific incubation time is critical to the result but the exact pipetting order isn’t, say so explicitly — this tells a trainee where deviation is safe and where it isn’t.
Have someone who didn’t write it try to follow it. This is the single most effective validation step and the one most often skipped. Hand the draft to a colleague who is competent in the lab but unfamiliar with this specific procedure, and have them perform it using only the document. Every place they hesitate, guess, or ask a question is a real gap in the SOP — not a training failure on their part.

Numbering, Version Control, and Approval

An SOP that exists as a loose Word document with no ID number and no version history is difficult to audit and easy to lose track of. Minimum document-control practice for a lab SOP library:

Unique ID and naming convention. Even a simple scheme (department code + sequential number, e.g. ‘MICRO-014’) lets an SOP be cited unambiguously from a protocol, grant report, or corrective-action record.
Version numbering and an effective date on every page — so a printed or downloaded copy can be checked against the current version at a glance.
A designated approver distinct from the author where possible — a lab manager, PI, or Chemical Hygiene Officer signing off adds a real second set of eyes rather than a formality. See CASRAI’s guide on writing and maintaining a Chemical Hygiene Plan for a closely related example of this same document-control discipline applied to a specific OSHA-required plan.
A retired/superseded version log — old versions should be archived, not deleted, and clearly marked as no longer in effect, particularly in any GLP or ISO-accredited environment where historical data may need to be traced back to the SOP version in force when it was generated.
Where practical, keep SOPs in a system with built-in audit trails — a document-management tool or, for the procedures they cover, an electronic lab notebook (ELN) that timestamps who accessed which version — rather than relying on shared-drive folders where an outdated copy can silently persist alongside the current one.

How Often to Review and Update SOPs

An SOP that’s never revisited drifts out of sync with actual lab practice, equipment, or regulatory requirements. Common practice is an annual review at minimum, with a documented review date and reviewer even when no changes are made — the review itself is the record that the document is still current, not just the edits. Trigger an out-of-cycle review whenever: equipment is replaced or its software/firmware changes materially; a near-miss, deviation, or nonconformance investigation points to the SOP as a contributing factor (this is where the SOP process connects to a lab’s broader CAPA (Corrective and Preventive Action) process); the underlying regulation or method reference is updated; or the procedure is being performed with any consistent, informal deviation from what’s written — which usually means the SOP is wrong, not that staff are careless, and is worth investigating either way.

Common Mistakes When Writing Lab SOPs

Copying a manufacturer’s manual almost verbatim. Equipment manuals describe everything the instrument can do; an SOP should describe only what your lab actually does with it, in your lab’s specific context (your reagents, your acceptance criteria, your safety controls).
No real owner. If no single person is accountable for keeping an SOP current, it’s guaranteed to go stale. Every SOP needs a named owner, not just an author of record from years ago.
Writing for an expert audience. An SOP that only makes sense to someone who already knows the procedure has failed at its main job, which is training someone who doesn’t.
Skipping the walkthrough validation step. An SOP that’s never been followed by someone other than its author frequently has gaps the author can’t see, because they’re filling them in unconsciously from memory.
No version control, or version control that isn’t enforced. Multiple copies of ‘the’ SOP floating around at different revision levels is one of the most common findings in internal and external audits.
Treating the SOP as a one-time deliverable. An SOP that’s written, approved, and then never reviewed again is a compliance liability waiting to surface at the next inspection or audit.

Lab SOP Template You Can Adapt

A minimal, reusable outline covering the sections above — adapt the level of formality to your lab’s actual regulatory context:

Title / SOP ID / Version / Effective Date / Author / Approver
Purpose and Scope
Responsibilities (who may perform this procedure)
Safety Information (PPE, hazards, required engineering controls)
Materials, Reagents, and Equipment
Procedure (numbered, single-action steps)
Quality Control / Acceptance Criteria
Troubleshooting
References
Revision History (version, date, summary of change, approved by)

Keep the template itself in the same document-controlled system as the SOPs it produces, so the blank template a new SOP is drafted from is also a known, current version.

Frequently Asked Questions

What is a lab SOP template?

A lab SOP template is a pre-built document skeleton — the header block, standard section headings (purpose, safety, materials, procedure, QC, references, revision history), and formatting — that a lab reuses every time it writes a new SOP, so every procedure in the lab’s library has a consistent, complete structure rather than being built from scratch each time.

How long should a lab SOP be?

As long as it needs to be to remove ambiguity from the procedure, and no longer. A short, well-scoped procedure (e.g., autoclave startup) might be one to two pages; a multi-day, multi-reagent assay with several quality-control checkpoints can reasonably run several pages. Length itself isn’t the measure of quality — a bloated SOP that repeats a manufacturer’s manual is worse than a tight one, and an SOP that’s too terse to actually follow without prior training has failed regardless of length.

Who should approve a lab SOP?

At minimum, someone with authority over the lab’s operations who did not author the document — typically a lab manager, PI, or a designated role such as a Chemical Hygiene Officer or Study Director, depending on the regulatory context. In GLP facilities, the study director’s authorization is required for any deviation from an approved SOP, which makes clear ownership and sign-off a real compliance requirement, not just good practice.

Do lab SOPs need to be reviewed every year?

There’s no single universal mandate that applies to every lab, but an annual review is the most common baseline in both regulated (GLP, ISO/IEC 17025) and unregulated academic lab settings, with additional out-of-cycle reviews triggered by equipment changes, incidents, or regulatory updates. The key practice is documenting that a review happened — with a date and reviewer name — even in years when no content changes were made.

What’s the difference between an SOP and a lab protocol?

In practice the terms overlap heavily, but where a distinction is drawn, an SOP is typically the standing, lab- or institution-level procedure for a recurring activity, while a protocol is often study- or experiment-specific and may simply cite the relevant SOPs by reference rather than restating their content. See CASRAI’s SOP dictionary entry for more on how this term is used across different lab and regulatory contexts.