Banana: The Banana as Unit of Measurement
The 'banana for scale' meme originated on Reddit circa 2009–2011 and uses the banana's standardized size (~19 cm for Cavendish) as an informal measurement reference. In radiation physics, the 'Banana Equivalent Dose' (0.1 μSv) is an accepted informal educational unit.
The 🍌 has a peculiar dual existence as both food and measurement instrument. Its consistent size makes it a reliable informal scale reference, and its potassium content gives it legitimate standing as a unit in radiation safety education. No other food occupies the same intersection of internet culture and physics pedagogy.
Banana for Scale: Meme Origins
The phrase “banana for scale” emerged from Reddit, specifically the community r/Whatisthisthing, where users post photographs of unidentified objects for crowd identification. The problem of scale in photographs — objects that could be 5 cm or 50 cm without a reference — prompted users to place familiar objects beside mystery items for size comparison. The banana became the preferred reference object for several reasons: it has a distinctive, instantly recognizable shape; it is consistently available in most households; and the Cavendish variety dominates retail globally with relatively standardized dimensions.
The practice was sufficiently widespread by 2011 that “banana for scale” appeared as a recognizable internet convention, generating derivative memes, scientific papers citing the informal standard, and even a dedicated subreddit (r/bananasforscale). The humor derives partly from the banana’s absurdity as a reference unit and partly from the genuine utility it provides.
Actual Standardized Dimensions
A commercial Cavendish 🍌 sold at retail in the United States or Europe falls within a reasonably narrow size range. The following table gives measured dimensions for Cavendish bananas across retail grades:
| Measurement | Minimum (Class II) | Typical (Class I) | Maximum (Class Extra) |
|---|---|---|---|
| Length (outer curve) | 14 cm | 17–20 cm | 22+ cm |
| Diameter (midpoint) | 27 mm | 32–38 mm | 44+ mm |
| Mass (with peel) | 80 g | 120–160 g | 200+ g |
| Mass (peeled) | 55 g | 90–120 g | 145+ g |
| Inner curve radius | ~5 cm | ~7 cm | ~10 cm |
The EU’s Commission Regulation 2257/94 — frequently cited in the myth that the EU “banned” curved bananas — actually only required that Class Extra and Class I bananas be “practically free from curvature defects,” meaning abnormal or exaggerated curvature. Normal banana curvature, which averages 40–60° of arc, was never regulated. See Banana Curvature Math for the geometric analysis.
The Banana Equivalent Dose
In radiation safety education, the Banana Equivalent Dose (BED) is an informal unit representing the radiation dose a person receives from eating one 🍌. A medium banana contains approximately 422 mg of potassium (see Banana and Potassium), of which 0.0117% is the naturally radioactive isotope potassium-40 (K-40), emitting roughly 14–15 becquerels of activity (see Banana Radioactivity).
One BED is approximately 0.1 microsieverts (μSv) — the effective radiation dose from ingesting a single banana. This is not an official SI unit, but the Health Physics Society and many nuclear safety educators use it to contextualize low-level radiation exposure.
| Activity | Approximate Dose | Bananas Equivalent |
|---|---|---|
| Eating one banana | 0.1 μSv | 1 BED |
| Chest X-ray | 20–100 μSv | 200–1,000 BED |
| Transatlantic flight (London–NYC) | 40–80 μSv | 400–800 BED |
| Annual background radiation (US average) | 3,100 μSv | 31,000 BED |
| CT scan (chest) | 7,000 μSv | 70,000 BED |
| Hiroshima survivor at 1 km | ~100,000 μSv | 1,000,000 BED |
It is important to note a caveat: the BED comparison overstates the hazard of banana consumption. Potassium is homeostatically regulated in the human body — excess potassium is excreted, meaning eating extra bananas does not meaningfully increase the K-40 burden in the body. External or accumulated doses are not equivalent to dietary potassium in terms of biological risk.
Other Banana-Based Units in Use
The 🍌🍌 appears in science communication for several measurement purposes beyond radiation:
| Unit Being Measured | Banana Reference | Notes |
|---|---|---|
| Length | 1 banana ≈ 19 cm | Consistent for adult Cavendish |
| Mass | 1 banana ≈ 120–150 g | Peeled weight |
| Carbon footprint | 1 banana ≈ 80–100 g CO₂eq | Per fruit, farm to retail |
| Energy content | 1 banana ≈ 100 kcal | Useful for dietary comparisons |
| Potassium dose | 1 banana = ~422 mg K | 9% of US daily recommended value |
Science communicators at institutions including NASA and the BBC have used banana units in public-facing content precisely because the object is universally familiar and dimensionally consistent across global retail markets.
🍌🍌🍌