Dress Size Calculator

Background.

A dress size calculator turns three tape measurements — bust, natural waist and hip — into a size number in whichever country's numbering you are shopping in. The awkward truth it has to work around is that dress sizes are not standardised anywhere. The United States withdrew Voluntary Product Standard PS 42-70, "Body Measurements for the Sizing of Women's Patterns and Apparel", and never replaced it with a government standard; what exists in its place is ASTM D5585, a voluntary industry table that no brand is obliged to follow and that is sold rather than published. So a calculated size is a coordinate to look up on a retailer's own chart, not a number you can order against blind.

What does have a documented structure is the continental European scale, and that is the scale this page works in internally. EN 13402-3, the European standard for size labelling based on body measurements, sets girth intervals of 4 cm with a tolerance of ±2 cm. Continental size 38 is drawn against a body of roughly 88 cm bust, 72 cm waist and 96 cm hip, and each 4 cm of girth moves you two size numbers. Invert that and you get three parallel relations with the same slope — half a size number per centimetre — one for each measurement. Every other series on this page is then a fixed offset from the continental number: subtract 30 for the US, subtract 26 for the UK and Australia, add 2 for France and Spain, add 6 for Italy. The published anchor everyone agrees on, continental 38 = FR 40 = IT 44 = UK 12 = AU 12 = US 8, falls straight out of those offsets.

The part most size charts skip is that your three measurements will usually not agree with each other, and the page reports all three answers rather than hiding the disagreement. Almost nobody sits exactly on the reference block: a body with an 84 cm bust, a 64 cm waist and 108 cm hips implies continental 36 from the bust, 34 from the waist and 44 from the hip — a ten-unit spread, or five US sizes. The rule for a single-piece garment is to buy for the largest of the three, because a seam can be taken in but not let out, and this page names which measurement that is and reports how far apart the three sit. When the spread is four continental units or more it says so explicitly, and suggests separates, because no dress cut on a standard block is going to fit that body without alteration.

A second thing worth knowing before you trust any conversion is that US labels have drifted. The number on an American garment describes a larger body today than the same number did when PS 42-70 was written, which is why a US brand's own chart will often place you one or two sizes below the conversion here. That drift is not folklore: Kinley, publishing in the Clothing and Textiles Research Journal in 2003, measured 1,011 pairs of women's trousers and found inconsistency in every single size category, with as much as eight and a half inches of waist variation inside one nominal size. Expensive garments measured larger than cheap ones at the same label. Against that background, a calculated size is a genuinely useful starting point and a genuinely poor substitute for a brand's centimetre table.

What this page deliberately does not do is worth stating plainly. It does not model height, so it will not tell you whether to buy petite, regular or tall — that is a separate grading axis and EN 13402-3 handles it in 8 cm height intervals rather than girth. It does not model shape beyond the three girths: shoulder width, back length, bust apex height, arm girth and the difference between a straight and a curvy grading all affect fit and none of them are inputs here. It does not know anything about a specific garment's ease, cut or fabric stretch, which between them can easily be worth a size in either direction. And it does not cover juniors', maternity or children's sizing, all of which are graded on entirely different blocks; measurements below the adult range are refused rather than silently labelled.

Used for what it is — a fast, transparent conversion from three girths to a starting size in six national series, with its own assumptions and tolerances printed beside the answer — it will save you the guesswork of reading six different charts, and it will tell you which of your measurements is the one that matters.

What is dress size calculator?

A dress size is a single number standing in for a whole body. Every national series picks a reference body for each number and grades outward from it in fixed steps, and the numbers themselves are just labels on those steps: continental 38, UK 12, US 8, Italian 44 and French 40 all point at approximately the same body. ISO 8559-1:2017 defines the anthropometric measurements themselves — how to locate and take a bust, waist and hip girth — and EN 13402-3:2017 defines how a European label should express them, using body dimensions in centimetres with girth intervals of 4 cm.

What no standard does is bind a manufacturer. In Europe, EN 13402 labelling is voluntary and widely ignored in favour of house numbering. In the United States, the government standard was withdrawn and the replacement is a purchasable ASTM table. That is why the same labelled size varies between brands, why it has drifted over decades, and why every serious retailer publishes its own centimetre chart alongside the size number.

The practical consequence is that a dress size is best treated as a search key rather than an answer. Calculate it, use it to find the right row of the brand's chart, then compare your actual centimetres against theirs — and buy for whichever of your three girths is largest.

How to use this calculator.

1. 01Pick your unit and use it for all three measurements.
2. 02Measure your bust: tape level all the way round the fullest point, over an ordinary unpadded bra, arms down, without pulling tight.
3. 03Measure your natural waist: the narrowest part of the torso, usually about an inch above the navel. Bend sideways — the crease that forms is the right level. This is not where your trousers sit.
4. 04Measure your hip: tape level round the fullest part of the seat and hips with your feet together, usually 18–22 cm below the natural waist.
5. 05Choose the country whose sizes you need. The same body is a UK 12, a US 8, a continental 38, a French 40 and an Italian 44.
6. 06Read the headline size, then look at the three per-measurement sizes underneath. If they disagree, the largest one is your size for a single-piece garment.
7. 07Check the spread warning. If your three measurements span four or more continental units, a dress cut on a standard block will need alteration, and separates will usually fit better.
8. 08Open the brand's own centimetre chart and match your measurements against it. Treat the calculated number as the row to look at first, not the final answer.

The formula.

Everything is computed in centimetres, because that is the unit the continental scale is defined in; inch inputs are converted first. Three estimates are then produced in parallel, one per measurement. The continental reference block puts size 38 at a bust of 88 cm, a waist of 72 cm and a hip of 96 cm, and moves two size numbers for every 4 cm of girth — that 4 cm interval is EN 13402-3's own mandated girth interval, which is why the slope is exactly half a size number per centimetre in all three relations. Solving each for the size gives bust ÷ 2 − 6, waist ÷ 2 + 2 and hip ÷ 2 − 10.

The size you are told to buy is the largest of those three, and the rounding stage matters here. The classification scalar is the maximum of the three unrounded values; it is rounded to the nearest even number, half-up, exactly once. Nothing is rounded for display and then classified again. Each per-measurement size is rounded the same way for its own output, but those rounded numbers are never fed back into the decision — which is why the page can correctly tell you the waist is driving your size even when the bust rounds to the same number. The boundaries are exact and tested: a bust of 89.9 cm gives continental 38 and 90.0 cm gives 40; a waist of 73.9 cm gives 38 and 74.0 cm gives 40; a hip of 97.9 cm gives 38 and 98.0 cm gives 40.

Cross-series conversion is a single addition. US = EU − 30, UK = EU − 26, Australia and New Zealand = EU − 26, France and Spain = EU + 2, Italy = EU + 6. These reproduce the anchor row every published chart agrees on: continental 38 = FR 40 = IT 44 = UK 12 = AU 12 = US 8.

Worked through with the page's own example: a body of 92 cm bust, 76 cm waist and 104 cm hip gives 92 ÷ 2 − 6 = 40 from the bust, 76 ÷ 2 + 2 = 40 from the waist, and 104 ÷ 2 − 10 = 42 from the hip. The maximum is 42, which is already even, so the continental size is 42 and the US size is 42 − 30 = 12. The hip is the driving measurement; the bust and waist each imply US 10. The two-unit spread is inside EN 13402-3's own ±2 cm girth tolerance, so no proportional-mismatch warning is raised — but the page still tells you the hip is what put you in a 12.

A worked example.

Frequently asked questions.

References& sources.

1. [1]European Committee for Standardization, EN 13402-3:2017 — Size designation of clothes, Part 3: Size labelling based on body measurements and intervals. Establishes girth intervals of 4 cm with a tolerance of ±2 cm and height intervals of 8 cm (±4 cm); Annex A gives informative body-measurement tables for women, men and children. Sold by CEN national members; abstract and scope consulted, not the full text.
2. [2]International Organization for Standardization, ISO 8559-1:2017 — Size designation of clothes, Part 1: Anthropometric definitions for body measurement. The authority for how bust girth, waist girth and hip girth are located and taken. Sold by ISO; catalogue entry consulted.
3. [3]National Institute of Standards and Technology, "Withdrawn DOC Product Standards (PS)" — lists PS 42-70, Body Measurements for the Sizing of Women's Patterns and Apparel, among the withdrawn US Department of Commerce product standards, alongside PS 36-70 (boys'), PS 45-71 (young men's) and PS 54-72 (girls'). There is no current US government apparel sizing standard.
4. [4]ASTM International, ASTM D5585-21 — Standard Tables of Body Measurements for Adult Female Misses Figure Type, Size Range 00–20. The voluntary industry table that inherited the withdrawn PS 42-70 data set. Sold by ASTM; designation, title and scope consulted. Its measurement values are deliberately not reproduced on this page because they could not be retrieved from the standard itself.
5. [5]Kinley TR. "Size Variation in Women's Pants." Clothing and Textiles Research Journal 2003;21(1):19–31. doi:10.1177/0887302X0302100103. Measured the waist, crotch and inseam of 1,011 pairs of women's trousers and found inconsistency in every size category, with expensive garments generally measuring larger at the same nominal size.
6. [6]ASTM International, Subcommittee D13.55 on Body Measurement for Apparel Sizing — the committee of record for US voluntary apparel sizing tables, and confirmation that these tables are consensus industry documents rather than regulation.