SNIP: Source Normalized Impact per Paper

SNIP (Source Normalized Impact per Paper)

Source Normalized Impact per Paper (SNIP) is a journal-level citation metric calculated from Scopus data by the Centre for Science and Technology Studies (CWTS) at Leiden University -- not by Elsevier, despite appearing alongside Elsevier's own CiteScore on Scopus source pages. SNIP measures citations received in a given year to a journal's publications from the preceding three years, divided by the number of those publications, then normalizes that ratio by the citation potential of the journal's subject field, correcting for the fact that citation practices (typical reference-list length, citation density) vary sharply across disciplines.

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· Last updated 25 Aug 2026

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Worked examples

Is an instance

A librarian comparing journals across two very different fields (e.g., mathematics and cell biology) uses SNIP rather than raw citation counts or Journal Impact Factor, because SNIP corrects for the fields' very different baseline citation rates.

Is an instance

CWTS publishes SNIP values annually on journalindicators.com, independent of and in addition to Scopus's own display of the metric on source pages.

Looks similar, but isn't

Not an instance

Treating SNIP as an Elsevier product -- it is calculated by CWTS at Leiden University, an independent academic body, using licensed Scopus data, the same relationship SJR (SCImago Journal Rank) has to Scopus.

Not an instance

Using SNIP to rank individual authors or papers -- like other journal-level metrics, SNIP describes a journal's field-normalized average, not any single article's or researcher's citation performance.

SNIP (Source Normalized Impact per Paper) is a field-normalized, Scopus-based journal-level citation metric, originally developed by Henk F. Moed at the Centre for Science and Technology Studies (CWTS), Leiden University, and first published in 2010, with a revised methodology introduced in 2012.

Last verified August 25, 2026 against CWTS’s Journal Indicators methodology page and the peer-reviewed SNIP literature.

Who Calculates It

SNIP is calculated by CWTS at Leiden University using licensed Scopus citation data, and published on CWTS’s own journalindicators.com site as well as displayed on individual journal pages within Scopus itself. This makes SNIP’s institutional relationship to Elsevier the same as SJR‘s: both use Scopus data under license but are computed independently of Elsevier, unlike CiteScore, which Elsevier calculates and publishes itself.

How It Is Calculated

SNIP is the ratio of a journal’s raw citation impact to the citation potential of its subject field:

Raw citation count. Citations received in the present year to the journal’s publications from the preceding three years, divided by the number of those publications — a three-year citation/publication ratio.
Field normalization (citing-side). Unlike metrics that normalize by classifying each journal into a fixed subject category, SNIP normalizes based on the characteristics of the citing publications themselves: the longer a citing paper’s reference list, the lower the weight assigned to any single citation it contributes. Fields where papers typically cite more sources (and where citations therefore accumulate faster across the literature) get a correspondingly lower per-citation weight, and fields with sparser citation practices get a higher one.

The practical effect is that a journal in a field with naturally low citation density (for example, mathematics) is not penalized relative to a journal in a field with naturally high citation density (for example, cell biology) purely because of how each field’s researchers cite. In Scopus, the citation-weighted average SNIP value across all covered journals is calibrated to 1.000, so a SNIP above 1 indicates above-average impact relative to the journal’s field, and below 1 indicates below-average.

SNIP, CiteScore, and SJR: Three Scopus-Derived Metrics

SNIP is one of three journal metrics that appear together on Scopus source pages but come from different sources and use different logic:

	SNIP	CiteScore	SJR
Calculated by	CWTS, Leiden University	Elsevier	SCImago Research Group
Citation window	3 years	4 years	3 years
Field adjustment	Citing-side normalization by field citation potential	None (raw citations per document)	PageRank-style weighting by citing-source prestige, not raw field normalization
What it’s designed to answer	“How does this journal’s citation impact compare once its field’s citing behavior is accounted for?”	“How many citations, on average, do this journal’s documents receive?”	“How prestigious are the sources citing this journal?”

See the CiteScore entry and the CiteScore vs. SJR comparison for how the other two metrics in this trio are built; SNIP’s distinguishing feature among the three is that it normalizes for field-level citation density specifically, which SJR and CiteScore do not attempt in the same way.

Why Responsible-Assessment Guidance Treats It the Same as Other Journal Metrics

Despite its field-normalization design, SNIP remains a journal-level average and is subject to the same critique DORA and CoARA apply to journal-level metrics generally: it describes the citation behavior of a journal’s article population, not the quality or eventual impact of any individual paper or author within it, and neither body endorses substituting it for direct evaluation of a specific work in hiring, promotion, or funding decisions.

Why This Matters for Research Administration

For research administrators supporting cross-disciplinary hiring or tenure committees, SNIP’s field normalization makes it one of the more defensible journal-level comparisons to surface when a committee insists on citing a metric across candidates from very different fields — though the underlying caution against using any journal-level metric as a proxy for an individual researcher’s work still applies in full.

Frequently Asked Questions

Is SNIP an Elsevier metric?

No. It is calculated by CWTS at Leiden University using licensed Scopus data. Elsevier displays it on Scopus source pages but does not calculate it, the same relationship Scopus has to SJR.

What does a SNIP value above 1.0 mean?

The journal’s field-normalized citation impact is above the average across all journals Scopus covers, since Scopus calibrates the overall weighted-average SNIP to 1.000.

How is SNIP different from CiteScore?

CiteScore is a raw four-year citations-per-document ratio calculated by Elsevier with no field adjustment. SNIP uses a three-year window and applies citing-side field normalization, and is calculated by CWTS, not Elsevier.

Can SNIP be used to evaluate an individual researcher?

No. Like other journal-level metrics, SNIP describes a journal’s average field-normalized citation impact, not any individual article’s or author’s citation performance — DORA and CoARA both caution against using journal-level metrics as a substitute for evaluating individual work.

References

CWTS, Leiden University, “Journal Indicators – Methodology” (journalindicators.com).
Moed, H.F., “Measuring contextual citation impact of scientific journals,” Journal of Informetrics, 2010.
Waltman, L. et al., “Some modifications to the SNIP journal impact indicator,” Journal of Informetrics, 2013.

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