---
title: "Effective Content Units (ECU)"
description: "Review-mass normalization across prose, code blocks, tables, diagrams, math, and HTML/MDX."
keywords: ["effective content units", "ecu", "review mass", "documentation size"]
---

**ECU** normalizes review mass so that a small-but-dense ADR is not overshadowed by a long linear README
in volume comparisons. It blends prose word count with weighted contributions from code, tables,
diagrams, math, and raw HTML/MDX.

## Formula

```text
ECU = W / 240
    + 0.35 · CLOC
    + 0.06 · table_cells
    + 0.40 · diagram_nodes
    + 0.25 · diagram_edges
    + 0.12 · math_tokens
    + 0.20 · raw_html_or_mdx_lines
```

The `W / 240` term anchors on the standard adult silent-reading-rate scale (~240 words per minute).
Other coefficients are derived to make a small, dense diagram contribute roughly as much as the
equivalent paragraph of explanation.

## Interpretation bands

| ECU | Meaning |
|---|---|
| `< 5` | Small. |
| `5–20` | Normal. |
| `20–60` | Large. |
| `> 60` | Documentation subsystem — likely wants a split. |

## Why not just word count?

Word count systematically undercounts artifact-heavy docs (architecture diagrams, big tables, code-only
references) and over-weights prose-heavy docs that may be relatively easy to skim. ECU was introduced so
"dense vs. linear" shows up directly in volume comparisons.

## References

- Trauzettel-Klosinski, S. & Dietz, K. (2012). *Standardized assessment of reading performance: the
  new International Reading Speed Texts IReST.* Investigative Ophthalmology & Visual Science 53(9):
  5452–5461 — the silent-reading-rate evidence base that anchors the `W / 240` term.
  [DOI](https://doi.org/10.1167/iovs.11-8284).
- Brysbaert, M. (2019). *How many words do we read per minute? A review and meta-analysis of reading
  rate.* Journal of Memory and Language 109: 104047.
  [DOI](https://doi.org/10.1016/j.jml.2019.104047).

## See also

- [LOC family](/metrics/markdown/loc-family) — components that feed ECU.
- [Section tree](/metrics/markdown/section-tree) — per-section ECU aggregation.
