What a 1-inch grid actually is

1. Where the inch comes from

The grid on a battle mat is not a decorative pattern, it is a unit of distance. In fifth edition Dungeons & Dragons one square is five feet, so a thirty-foot move is six squares and a spell with a twenty-foot radius reaches four squares from its centre. Pathfinder works the same way. The whole point of a grid is that nobody has to argue about how far anything got.

The square is an inch across because a medium creature’s miniature is about an inch across at the base. One mini, one square, no overhang. That is the entire design brief, and it is why the inch survives on a product sold almost everywhere in the world in centimetres.

2. 25.4, not 25

One inch has been exactly 25.4 mm since 1959, when the English-speaking countries agreed to define it against the metre. It is not an approximation, and there is no version of it that is 25.

So the convenient shortcut — call it 2.5 cm, it is close enough — costs 0.4 mm per square. On one square that is invisible. It does not stay on one square:

• 1 square: 0.4 mm short. Nobody alive can see it.
• 10 squares: 4 mm short. A ruler shows it plainly.
• 27 squares: 10.8 mm short — more than a third of a square has evaporated across the width of the mat.

That is the practical failure. A mini that sits neatly inside the first square on the left sits noticeably proud of the line near the right-hand edge, and a distance counted in squares stops matching a distance measured with anything else. It is not a printing defect. It is arithmetic that was settled before the file was made.

3. Why a metric mat cannot come out even

Divide the mat by the inch and the problem is immediate. A 40 × 70 cm mat holds 27.56 squares along its long side and 15.75 across the short one. Neither is a whole number, and no amount of care at the press will make them one.

Which leaves a maker exactly two choices, and only two:

• Keep the inch and accept a ragged edge. The grid is correct everywhere, and the outermost column and row are partial squares. The mat looks slightly unfinished at the border.
• Keep the round number and shrink the square. Fit 28 columns into the 700 mm side and each one is 700 ÷ 28 = 25.0 mm exactly. Fit 16 rows into the 400 mm side and you get 25.0 mm. The mat looks immaculate, the corners come out perfect, and the grid is not an inch.

Read that second number again, because it is the most useful thing on this page. A 40 × 70 cm mat advertised as 16 × 28 squares is a 25 mm mat. The listing is not necessarily lying — it may never mention inches at all — but if it claims a 1 inch grid alongside a whole number of squares that divides evenly into a metric size, those two claims cannot both be true.

The same test works at any size. Whenever the advertised square count divides the advertised millimetres into a clean round number, the square has been rounded to fit. A real inch leaves a remainder, every time.

And before any of this matters, there is a bigger fork: a blank grid you draw on, or a printed scene you play on. They share a name and they are not the same purchase.

4. Checking a mat you already own

This takes ten seconds and needs nothing but a steel rule, or a tape measure with millimetres on it.

Do not measure one square. A single square is somewhere near 25 mm either way, and the 0.4 mm you are hunting is thinner than the printed line itself. Measuring one square cannot answer the question.

Measure ten. Lay the rule down the middle of one grid line and read the middle of the line ten squares along, in the flattest part of the mat, away from the edge.

• 254 mm — a true inch grid.
• 250 mm — 25 mm squares. Tidy, common, not an inch.
• Anything else — divide by ten and you have your actual square, whatever the listing said.

Twenty squares makes it harder still to misread: 508 mm for the real thing against 500 mm for the rounded one. Half a centimetre is not a matter of opinion.

No steel rule in the house? Print our strip instead — ten squares at a true inch on one sheet of A4, with a 100 mm bar at the top so you can check your printer before you trust the strip.

One fair warning about any printed mat, ours included. Cloth and rubber are printed with a little stretch and settle differently once rolled and unrolled, so a millimetre either way across ten squares is manufacturing, not deception. Four millimetres is not manufacturing.

5. What we did, and what we cannot claim yet

We took the first branch in section 3. Our print file lays 5,376 pixels along the 700 mm side, which puts one inch every 195.072 pixels and gives 27.56 × 15.75 squares. The outer column and row are partial on purpose. We would rather hand you a real inch with a cut edge than 28 tidy squares that are not inches.

Everything else about the mat — what it is made of, how long it takes, and what shipping and import VAT are included in the price — is on the shop page, and set out in full in the terms of sale.