# The lines on a jug get closer together on purpose

> A measuring jug tapers, so equal volumes take up less height near the top. The closing gap between its graduations is arithmetic somebody worked out once, in glass.

August 19, 2026 · https://justog.club/stories/measuring-jug-lines

A jug's outline, drawn flat and empty. Up one edge, 100, 200, 300, 400, 500. Up the other, 4, 8,
12, 16. The gaps between the lines shrink as they climb; the 500 mark, near the top, is picked out
in red.

Nobody ruled those lines evenly. Somebody worked out where each one had to go.

## Why aren't the lines evenly spaced?

Because the jug isn't a cylinder — it's narrower at the bottom than it is near the rim.

A given rise in liquid level fills a smaller volume in a narrow bottom than it does further up
where the glass has flared out, so the same 100ml gap has to be marked taller down low and shorter
near the top to stay accurate. The closing spacing isn't a printing quirk. It's the shape of the
jug, translated into a ruler.

## Why does the arithmetic happen on the jug instead of in the cook's head?

Because somebody already did the sum, once, at the factory, so nobody has to do it again at a
worktop.

Working out how far up a tapered vessel 300ml actually sits means knowing the jug's exact profile
at every height — not something anyone wants to calculate while a pan's already on. Printing the
answer straight onto the glass moves the arithmetic from every kitchen, every time, to one drawing
office, once. It's the same move a [timing chart taped over an oven](/stories/oven-timing-chart)
makes, working backwards from a serving time so nobody reruns the sum on a Sunday.

## What makes a good jug worth drawing?

Two full scales, honestly spaced, rather than one dressed up as two.

A jug carrying both millilitres and fluid ounces up its own edges is a small confession that the
household using it hasn't fully picked a system — a common enough state that most jugs sold still
carry both. The red on the 500 line does the same job the ounces do lower down: it's the mark
somebody actually reaches for, picked out because it's the one that gets used.

## Can I put a real glassware brand's markings on it?

Not their design or their name, though a calculated scale isn't anybody's to own.

Working out where a line falls on a tapered vessel is physics, not intellectual property — every
manufacturer does the same sum and none of them owns the answer. A specific brand's jug shape,
logo or the exact wording on its base are theirs, worth asking about if that particular jug is the
point. An invented profile does the same job without the question.

## Does this apply beyond a kitchen jug?

Anywhere a tapered vessel needs a scale calculated rather than ruled.

Laboratory measuring cylinders, medicine cups and fuel gauges on an irregular tank all carry the
same problem and the same fix — a printed scale that accounts for the container's actual shape
instead of assuming it's a straight-sided tube.

## Isn't a printed scale just a ruler — nothing worth a second look?

Only if you assume the marks are evenly spaced, which is exactly the part people get wrong.

Most people who've used a jug for years have never noticed the gaps closing near the top; they just
pour to the line. The interesting part isn't the ruler, it's that the ruler had to be worked out
rather than measured with a tape — the same quiet calculation behind a [wrapper that measures
butter by where you cut it](/stories/butter-paper-weights), just solved with a curve instead
of a straight edge.

## Does it print well?

Yes — a clean outline with two ladders of numerals is a strong, legible shape at any size.

Keep the jug's profile in a single confident line and hold the red to the one mark that earns it;
crowding both scales too close together will blur at fabric scale, so give the millilitre and ounce
columns enough air between them to read as two separate ladders, not one smudged one.

## How do I get one made?

Describe the jug at [JustOG](/) — which scale to run up which edge, and which line to pick out.
Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to
order and shipped.

Designs other people have published are in the [shop](/shop).

Five hundred millilitres, marked near the top, where the same rise in the glass now means more
liquid than it did at the bottom.