Diamond vs Heart Face Shape: Three of the Five Checks Are the Same Number

Five checks, two rows, one table

The rule set behind every number on this page is published in full on the about page: five checks, seven rows, one standard deviation per check, one weight per check. The two rows below are copied out of it rather than measured for the occasion, which is the only honest way to say where they come from. Each check is one length divided by another, so the units cancel and nothing in this table is in centimetres or inches.

The tolerance column matters as much as the centres. A spread of 0.18 on the length ratio is a pooled within-group standard deviation taken from a set of 50 photographs, and every band on this page is one of those deviations either side of the centre. Two of the centres here deserve a specific caveat: the heart row rests on one photograph in that set and the diamond row on three, and their positions were placed by taking the order published in the literature and spacing it across the range the detector actually measures. The about page says the same thing.

Read the last column before reading the numbers. Three of the five rows do not move at all between the two shapes.

One standard deviation is a chosen band width, not a natural boundary; widening it to two changes some of what follows, and where it changes something this page says so. The two widths at the top of the face have a millimetre version worked out elsewhere on this site, in the glasses guides for a heart face and a diamond face; it is not repeated here because repeating the arithmetic is how two pages end up disagreeing about one face.

Three of the five are the same number, and not because of rounding

Counting those matching cells is the part worth stopping on. Seven rows taken two at a time is twenty-one pairs, and you can count, for each pair, how many of the five checks print exactly the same value for both. Doing that count over the published table gives one pair at three, two pairs at two, two pairs at one, and sixteen pairs at none:

The remaining sixteen pairs share no value on any check. This count is of printed cells in the rule set; it is a different thing from the distances between shapes, which are worked out on their own page.

Why the equality is not an artefact of the units

The table above is in tape units because that is what a reader can check at home. The classifier does not work in tape units; it works in the raw proportions a face photograph gives, and a fixed conversion carries one to the other. Run the same equality count on the raw scale and it lands in the same place: the jaw ratio is 0.76 for both shapes there, the jaw angle 135°, the chin taper 0.39.

The reason is structural, not a coincidence waiting to be explained away. The conversion is a single straight-line map applied to the centres and the spread together, which is why a tolerance of 0.18 in tape units and 0.048 in photograph units describe the same band. Two rows that share a value on one scale share it on the other, and a difference of 0.27 spread on one scale is a difference of 0.27 spread on the other. The equality is a property of the rule set, not of the way it is printed.

So: everything below the cheekbones is, in this rule set, the same for both shapes. A jaw that measures 0.72 of the cheekbone width. A corner that turns at 120°. A chin that narrows to 0.30 of that jaw. Whatever else is true of these two faces, the lower half is not where the published numbers put the difference.

Two of those three rows deserve a discount, and this site has already published the reason. The jaw angle is the least clean separation in our own fifty photographs — it could not tell a round face from a square one, the two landing within a degree of each other where the literature puts them more than twenty degrees apart. The chin taper carries so little signal between groups on that set that its weight was cut to 0.49, the lowest of the five. Their agreement between heart and diamond is therefore not a discovery about faces; it is a record of what the rule set declines to use. Which leaves the length row and the forehead row, and the argument in the next two sections.

The length row is 0.05 apart inside a tolerance of 0.18

Diamond sits at 1.40 and heart at 1.35 on the length ratio. That direction is real — the ordering comes from the literature and holds on both scales — but look at what it is measured against. The spread within either row is 0.18. The distance between the two centres is 0.049, which is 0.27 of that spread. For scale, the widest gap anywhere between two rows on any single check in the published table is 3.29 spread, and of the twenty-one pairs, only one is closer on the length row than this pair, and it is closer because its two centres are the same number.

Drawn as bands, the two rows run 1.17 to 1.53 and 1.22 to 1.58. They share everything between 1.22 and 1.53: 0.315 of a band 0.365 wide, which is 86 per cent of either one. A length reading in that shared ground is consistent with both labels and eliminates neither. Here is the half of the sentence nobody finishes: the two shapes are not far apart on every measurement, and on the measurement guides lean on hardest, length, they are inside noise.

There is a trap here worth naming, because the about page publishes the number that makes it. The length ratio carries the highest weight of the five checks, 1.59, and the forehead ratio carries 0.97. Weights are fitted to separate all seven rows from each other at once, not to settle any particular pair, and this pair is the counter-example: the row with the most weight is the one that says nothing about whether you are heart or diamond, and the row with less of it is the only one that does. Reading a weight as a verdict for one pair is how people end up arguing from a number their own face does not produce.

The one row where the two bands do not touch

Forehead width divided by cheekbone width: 1.05 for heart, 0.80 for diamond. That is 0.25 of the cheekbone width apart, 3.09 times the within-row spread — the largest gap on this row in the published table, shared with exactly one other pair, because the triangle row sits on the same forehead value the diamond row does. Banded at one standard deviation the two rows run 0.97 to 1.13 and 0.72 to 0.88, and between 0.88 and 0.97 there is a strip 0.09 wide that belongs to neither label.

The same 0.09 appears on this site's inverted triangle page, in a comparison of heart against triangle. The repetition is not a second copy of the same argument: two different rows happen to share a forehead value, so the gap from heart to each of them is the same gap. Worth saying out loud, because a number that repeats across pages is a number a reader should be able to trace.

Say plainly what the strip is and is not. It is a one-sigma statement. Widen both bands to two standard deviations and heart's floor drops to 0.89 while diamond's ceiling rises to 0.96, so the two overlap and the no-man's-land closes. What does not depend on the band width is the direction and the size of the difference: at any reasonable band, the forehead row is the one on which these two shapes are furthest apart.

For a reader with a tape, none of this needs division. 1.00 on this row is the point where the forehead exactly equals the cheekbone width, and heart is the only one of the seven rows whose centre sits above it. So the question is not how much wider, which is what the published guides leave the reader to guess. It is which of the two widths is the larger — forehead across its widest, cheekbones across the tops, one number each, compared as themselves. The millimetres that comparison turns into on a working face width are calculated on this site's glasses guide for a heart-shaped face, and this page will not run that arithmetic a second time.

What your tape gives you, and what it does not

Enter the four lengths and this site runs all five checks against the table above, prints a margin for every row, and names a second shape when one sits close behind the first: Open the face shape calculator ↓

Five checks is the photograph path. A soft tape gives you three of them — length, forehead and jaw, each divided by the cheekbone width — and the calculator path is built around exactly that limit. Chin taper asks for the width of the chin at its narrowest, and the placement is ambiguous by enough millimetres to move the whole band, so the calculator has no field for it and drops the row to zero weight rather than feeding in a number nobody measured.

The jaw angle has the same problem in a different shape. Unless you enter a protractor reading yourself, the calculator estimates it from your three ratios: it classifies on the ratios first, then averages the published angle of each row against the probabilities it just got. Which means that on the tape path, the identical angle row of the first table is not a third piece of agreement. It is the same three numbers wearing a fourth name.

Subtract all of that and the tape reader's heart-versus-diamond question is two numbers: the length ratio, 0.05 apart and therefore useless, and the forehead ratio, 0.25 apart and therefore the one worth taking carefully. Take the jaw ratio for another reason: it is the number that confirms you are in this pair at all, because both rows sit low on it and a jaw near your cheekbone width puts you elsewhere in the table entirely.

The hairline is not one of the five

Every guide that answers this question in print reaches for the forehead, and a good number of them reach past it to the hairline: a widow's peak plus high cheekbones, a straight hairline plus a broad top, the hairline as the tiebreaker. It is a plausible feature. Pointed chin, wide top, narrow jaw is the silhouette a widow's peak sits on, and the two do travel together in real faces.

It is not, however, a field in this rule set. The five checks are length, forehead width, jaw width, the angle at the jaw corner, and chin width over jaw width. There is no hairline entry, no widow's-peak flag, nothing a photograph of your forehead's edge would enter. A reader told to decide this question by their hairline has been handed a criterion this site cannot check, cannot weight, and cannot tell you the tolerance of — which makes it, as far as these pages are concerned, a coin.

That is a limit on this page as much as on the guides. The hairline may be diagnostic; nobody has settled whether it is, because nobody has published a labelled sample with hairline entries against face-shape labels. What can be said is narrower and worth more: which of the criteria currently in print can be set against a published number, and which of them are words standing where a measurement should be.

Every published position on this border, oldest first

Nine positions that could be dated to a day, oldest first: 4 April 2018 to 21 September 2026, just over eight years — eight years and five months, to be exact. The third column is the one to read down.

Identities are given by type, not by name or link, for every row that is not this site. Dates are the publication date printed on the page, with the revision date where the page carries one. Two further results for this query show no date anywhere on the page and so cannot sit on a timeline; two are image collections that aggregate other people's pictures rather than a position anyone published; two returned nothing readable, to either of the two methods used. None of those four is a row above, and no sentence on this page rests on what they might have said. The search engine's own generated answer for this query places a three-row comparison at the top of the results with no number in any cell; it is a summary of the six rows above, not a source, and is not counted.

What moved in eight years, and what did not

Down the third column, one thing has not moved in eight years and five months: not a single position outside this site has ever put a number against this pair. Not a threshold, not a tolerance, not a table. The advice format stayed constant — a silhouette description, an ordering, or two widths to compare without saying where the comparison tips.

What did move is the direction. The 2018 page left it genuinely open inside its own sentence, giving heart a wider forehead and cheekbones without saying which of the two is wider. By 2025 the same source pool had closed it: forehead as wide as or wider than the cheekbones, then the ordering version of the identical rule. Eight years and five months of published answers, and the qualitative half got settled while the arithmetic stayed missing.

The three rows that carry numbers are all from September 2026, and two of them are this site. That is not a claim of superiority; it is a description of a gap. If you want the border as a number, there is exactly one published table that has one, and it is the one the first section of this page is cut from, with the limits printed under it.

If the two widths land between the rows

Take the forehead width and the cheekbone width as themselves. Forehead clearly wider: this is the row the heart label sits on, and the advice about the top of the head runs in the opposite direction from the diamond page. Forehead clearly narrower, cheekbones standing alone as the widest point: the diamond row. Both within 0.09 of each other — say a forehead ratio of 0.93 — and you are in the strip, and no amount of measuring harder will move you out of it, because the strip is what the published bands leave empty.

Being in the strip is not a failure to measure; it is the ordinary case for a face that is neither of these two rows exactly, and the answer is not to average the two pages' advice. The diamond hairstyle page already says why, in the section written for this exact situation: the two pages instruct opposite things at the top of the head, so a blend of them lands volume at the cheekbones, which is the one placement wrong on both shapes. Read that section rather than taking a little from each page, and keep the half that is safe whichever row you turn out to be.

The classifier handles the same situation in the open. It weighs all five readings at once and returns a margin against every row rather than a single word, and when the runner-up reaches 0.60 of the leading probability the result page says so and names both shapes. That is the honest shape of the answer here: on this pair, the margin comes from one row, and the row our own photographs separate least cleanly is not the one doing the separating.

• Pull the hair back off the forehead and hold your head level. A fringe lying across the forehead lowers the reading without changing the face.
• Take the forehead width across its widest point and the cheekbone width from the top of one cheekbone to the other, passing just under the eyes. Write the two numbers down before dividing anything.
• Compare them directly. Which is larger answers the heart-diamond question; how much larger is the part this site puts a band around.
• Take jaw width too, corner to corner, straight across. If your jaw measures close to your cheekbone width you are not in this pair, and reading further would be the wrong use of your time — the square and oblong rows are elsewhere.
• If the two widths land in the strip, style the half that is safe on either side and read the diamond hairstyle page's borderline section instead of merging the two.

What this page cannot prove

The centres on the heart row and the diamond row are not averages of measured faces. In the fifty photographs this site calibrated on, one was labelled heart and three were labelled diamond. Their positions come from taking the order the literature gives the seven shapes and spreading it across the range the detector measures, which is why they land where they do. Every gap on this page is therefore a gap between two published conventions that have been made internally consistent, not a measured difference between two populations. A face can be entirely consistent with both rows and be neither.

The tolerances come from four groups with five or more members in that same set of fifty — the pooled within-group spread, and it travels across all seven rows including these two. The fifty photographs were labelled by one person, with no second rater and no published inter-rater agreement. Nobody has checked whether a professional stylist, given the same fifty, would put the same labels on them.

The step nobody has taken is the perceptual one. This page says where your tape reading falls against a published table. It does not say that a stranger can see the difference, or that the 0.25 forehead gap reads as a different face rather than as a range of ordinary variation. There is no study here, ours or anyone else's, that maps these ratios onto what people actually judge, so any sentence on this page about what you look like would be a guess wearing a number.

What would change this page: labelled photographs at five or more per row, so the centres become measured instead of placed; a second rater over the existing fifty; or a perceptual result showing the forehead row is visible to other people. Until then the useful part is the comparison itself — two widths, which is larger — and the table's right-hand column, which is a record of what our own rule set uses and what it declines to use.

Questions this page answers