Fit perfectly every time.
An AI-powered size guide for apparel — measurements in, the right size out, across garments, brands, and regions. The newest instrument in the fit family, built on the method proven at Brasize.ai.
Try it
This is the product's core calculation, running live on this page — band from the snug underbust, cup from the bust-band difference, sister sizes either side.
Overview
An AI-powered apparel size guide extending the BraSize.ai fit engine to garments broadly — measurements to recommended sizes per brand, regional conversion, and fit diagnosis, built to cut returns and capture high-intent sizing queries.
Inside the product
Each card names a real element on the product and reproduces a sample readout from it, so the page shows the product rather than describing it.
The headline result: total daily energy expenditure, split into the share that is resting metabolism and the share added by movement and digestion.
Three ways in. Each shows only the inputs it needs — a cycle length for LMP, a transfer date and embryo age for IVF.
The signature element. Bleeding days are marked, the fertile window is bracketed, and a needle marks estimated ovulation. The dial centers on the next period in tracking mode.
Add/Subtract, Duration, From Now, Work Hours, Date, and Units share one input panel — switch mode, keep the rail.
Underbust, measured snug, becomes the band. Bust, measured loose at the fullest point, minus the band becomes the cup.
A few body measurements translated into a recommended size per garment type and per brand, with the reasoning shown.
Four calorie targets derived from the same maintenance line, each labelled with the pace of change it implies.
The signature element: three trimester zones, milestone ticks at 14, 20, 28, 37, and 40 weeks, a 'today' marker, and the estimated due date at the far end.
Next period, ovulation, fertile window, and today — each with a date and the days until it.
The signature element: a calibrated rail with the start, the span, and the result marked — the same drawing for every mode.
The same size shown in every system a shopper will meet, so an online order in a foreign brand lands right.
Apparel sizes across US, UK, EU, and international letter sizes, following the pattern of the Brasize.ai converter.
Protein set first to protect lean mass, then carbohydrate and fat divided across the remaining calories — with a one-tap copy of the full result.
Weeks and days since the gestational start, the current trimester, and days remaining — or days past the estimate.
Three calibrated cycles in one glance, so the reader sees a pattern instead of a single date.
Gross shift and paid hours in clock format and decimal, with the unpaid break subtracted correctly.
Sizes with the same cup volume on a different band, for when the band runs tight or loose in a given brand.
Symptom-led guidance — tight across the shoulders, long in the sleeve — and the direction to adjust.
A ±5–10% range drawn around the estimate, a list of what no formula can see, and a three-step calibration routine.
Four dating methods, including clinical ultrasound, with the input each needs, its formula, and a plain note on when it is the right choice.
Idealised estrogen, LH, and progesterone curves across a 28-day cycle, with the four phases explained alongside.
Add or subtract days, weeks, months, and years, with the resulting weekday shown so schedules are readable at a glance.
What a riding band, gaping cup, or digging wire means — and which direction to adjust.
The instrument family
Every calculator on the product runs on the same logic layer, so answers never disagree with each other. Numbered in the order the product presents them; instruments marked Soon are on the public roadmap.
Method
Every NativeCode product publishes its assumptions on the page. This is the sequence the engine follows.
Mifflin-St Jeor is the default, recognised by the Academy of Nutrition and Dietetics as the most accurate general-population equation.
The standard convention. It assumes a 28-day cycle with ovulation near day 14; a different cycle length shifts the estimate by the difference from 28.
A cycle is counted from the first day of bleeding to the day before the next bleed. The site projects three cycles, not one.
Every clock time is converted to total seconds, the change is applied, and the result is normalised back to a 12- or 24-hour clock, tracking day rollover.
The snug ribcage measurement is the band. The modern method does not add four inches — that rule dates from stiffer fabrics and is the most common source of wrong sizes.
Sizes vary by brand; bodies don’t. The guide anchors on a small set of measurements and maps them to each brand’s published chart.
The multiplier is the single biggest variable. The site tells people to match an average week, not a best one — a desk job plus four hard sessions is ×1.55.
Two weeks fewer than the LMP count — which is why 40 weeks from the last period is roughly 38 weeks of development.
The luteal phase holds near 14 days for most people while the follicular phase absorbs the variation — so counting backward is more reliable than the day-14 rule.
When an end time is earlier than the start, the calculator can treat it as the next day — so 11:00 PM to 2:30 AM reads 3h 30m.
A loose measurement across the fullest point. One inch of difference is an A, two is a B, three a C, four a D, then DD and beyond.
As on Brasize.ai, every recommendation shows which measurement drove it, so a between-sizes result is explainable rather than a black box.
Entering a body-fat percentage switches the engine to Katch-McArdle, which is driven by lean mass rather than total weight.
A day-5 blastocyst is transfer + 261 days. Because the embryo's age is known exactly, this is the most precise self-calculation available.
Sperm survive up to five days; the egg about one. Conception is likeliest in the final two days.
Thirty minutes is 0.5 hours, forty-five is 0.75. Every work-hour result shows both clock and decimal formats.
Band numbers change by system — inches, centimetres, or dress-size-style numbers — and cup ladders diverge above D. The converter handles both.
A stated methodology and editorial standard ship with the tools, not after them — the same rule applied across every NativeCode product.
Deficits and surpluses are applied to the maintenance line, with a low-calorie warning threshold of about 1,200 (women) and 1,500 (men).
A first-trimester crown-rump measurement is the most accurate dating method. When it disagrees significantly with LMP dating, clinicians rely on the ultrasound — and only a clinician sets the official date.
In an analysis of more than 600,000 cycles, only a minority were exactly 28 days. Entering real averages instead of defaults is what narrows the window.
Date math applies month lengths and leap years correctly rather than assuming 30-day months, and reports the day of week for the result.
Cup volume is relative to band. Going down a band and up a cup keeps the volume the same, which is how a shopper fixes a brand that runs tight.
Who it serves
One trustworthy calorie number and a macro split, without a sign-up wall.
A due date and a 'how far along' reading in seconds, without handing over a date to an app.
The next three periods and today's phase, without an account or a tracking pixel.
Paid hours from a shift, minus the break, in the decimal format payroll wants.
A size they can trust in the region and brand they are ordering from.
Confidence in a size before ordering from an unfamiliar brand.
A cited, reviewed reference to send clients instead of a spreadsheet.
Dating from transfer date and embryo age, not a last-period guess.
A fertile window that moves with cycle length instead of assuming day 14.
A date ninety days out, or the number of days between two dates, without a spreadsheet.
A diagnosis of the symptom and the direction to move — not just a number.
Fewer returns and a fit experience that increases engagement at checkout.
Definition-first answers to 15 high-intent questions about calories, BMR, and macros.
Ten quotable definitions and a three-method comparison written for direct citation.
Ten definition-first answers and six clinical thresholds that say when calendar math is the wrong tool.
A future date-difference, business-days, and time-zone API plus embeddable widgets.
Structured size, chart, brand, and conversion pages written as the canonical reference.
Canonical, structured apparel-size reference pages.
Trust
Reviewed by a board-certified family-medicine physician, with a named reviewer page and a last-reviewed date on the page itself.
Formulas follow the American College of Obstetricians and Gynecologists' Methods for Estimating the Due Date, with SMFM, NICHD, CDC, and OWH cited as supporting sources.
Methodology references ACOG patient guidance and large-scale cycle datasets published in peer-reviewed journals.
Calculations run in the browser. No account is needed and no personal data is collected or sent.
The measurement method, the cup ladder, and the regional conversions are documented on a dedicated methodology page.
The fit engine, converter pattern, and editorial standard are the ones already running on Brasize.ai.
Built on the peer-reviewed Mifflin-St Jeor (1990), Katch-McArdle, and revised Harris-Benedict (1984) equations.
Every calculation runs on the visitor's device. Nothing is stored or sent — there is no server to leak from.
Ranges are shown as ranges, estimates are labelled estimates, and the page says outright that it is not contraception.
Second-level arithmetic, correct midnight handling, and calendar-aware date math with leap years.
Guides are written and maintained under a published editorial policy, with a press page for citations.
No recommendation without a stated method — every result traces to a measurement and a published chart.
The page states the ±5–10% accuracy band and lists what a calculator cannot see — genetics, hormones, sleep, stress, NEAT.
The page repeats, wherever it matters, that an early ultrasound is the authority and that only a clinician sets the official due date.
Six readings — from 90 days without a period to bleeding between periods — are listed as reasons to see a clinician rather than keep tracking.
Every web calculator stays free. History, favourites, exports, and widgets are planned Pro features of the mobile app.
Snug-measure sizing rather than the 'add four inches' rule, which the site explains and retires.
SizeGuide.ai is the youngest NativeCode product; its toolset and reference pages are actively expanding.
Built by NativeCode
This product is structured the way answer engines read: a one-sentence answer at the top of every section, definition-first FAQs written to be quoted, formulas shown in full, and named sources. The same discipline we apply to client sites, applied to our own.
The case study
The agency view of the same product: what it is, why it exists, and what it demonstrates about the method we sell.
SizeGuide.ai is an AI-powered apparel size guide — body measurements translated into recommended sizes per garment and brand, regional size conversion, and symptom-led fit diagnosis. It is the second product in our fit and sizing family, built on the measurement-first method proven at BraSize.ai.
Wrong sizes drive the highest return rates in ecommerce, and sizing queries carry purchase intent that generic content cannot capture. We built SizeGuide.ai to extend a proven fit engine from one garment category to apparel broadly — for shoppers deciding at checkout and for the retailers who lose margin to returns.
That a fit engine, converter pattern, and editorial standard engineered once can compound across products. The measurement-to-chart mapping, structured size reference pages, and AEO answer formatting mirror the architecture we deploy on every client build competing for high-intent commercial queries.
FAQ
Total daily energy expenditure — the calories you burn in a day — plus your BMR, calorie targets for losing, maintaining, or gaining weight, and a suggested macro split.
Last menstrual period with adjustable cycle length, conception date, and IVF embryo transfer with day-3, day-5, or day-6 embryo age.
By subtracting the luteal phase — 14 days by default, adjustable — from the projected next period. On a 35-day cycle that lands around day 21, not day 14.
Add and subtract time, measure duration between two times, count work hours with breaks, calculate dates, convert time units, and more — in one workspace.
Two measurements — a snug underbust and a loose bust at the fullest point — in inches or centimetres.
It translates body measurements into recommended apparel sizes per garment and brand, converts sizes across regions, and diagnoses fit problems.
Mifflin-St Jeor by default. If you enter a body-fat percentage it switches to Katch-McArdle, which uses lean body mass.
No. Calculations run in the browser and nothing is transmitted or stored.
No. The site is explicit that a calendar calculator is an awareness tool, not contraception, and its avoid-pregnancy mode shows estimated risk only.
Yes. When the end time is earlier than the start, it is treated as the next day, so overnight spans are measured correctly.
US, UK, EU, AU, and FR, with band, cup, full size, and sister sizes.
It is the second product in the fit and sizing family and shares Brasize.ai’s engine, converter pattern, and editorial standard.
Yes. Every calculator on tdee.co is free, with no account, sign-up, or ads.
It is a strong center point, not a guarantee — only about 1 in 20 babies arrive on the estimated date. A first-trimester ultrasound is the most accurate dating method.
No. Every calculation runs in the browser; nothing is transmitted, stored, or tracked.
The work-hour tools produce decimal-hour totals in the format payroll systems use. The site advises confirming against an employer's official timekeeping policy.
A size with the same cup volume on a different band — a 34C, 32D, and 36B hold roughly the same volume.
US, UK, and EU numeric sizes plus international letter sizes, with more brand charts added as the reference grows.
Typically within 5–10% of true daily burn. The site recommends holding the target for two to three weeks and adjusting by 100–200 calories against the weight trend.
The companion iPhone app in development for tracking pregnancy weeks, appointments, symptoms, milestones, and cycle history.
With regular cycles, typically within a day or two. With irregular cycles the site tells you to read each date as the center of a window.
Both are in design on the same engine — a premium offline-first app and a date/time API with embeddable widgets. Neither is available yet; the website is the product today.
That rule dates from an era of non-stretch fabrics and produces bands that are too loose. The modern snug-measure method is more accurate.
Yes — like every NativeCode instrument, the core tools are free with no sign-up.
A board-certified family-medicine physician. The reviewer, credentials, and last-reviewed date are published on the page.
Independent medical review is pending; the site says so on the page and describes the content as general information, not medical advice.
Review by a board-certified OB-GYN is in progress; the reviewer byline publishes at launch, and the page says so.
Yes. Every calculator on the website is free with no account required.
Yes, with no sign-up.
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