How SmartSize picks the right size for your shoppers
This page walks through what happens behind the scenes every time a shopper uses your size quiz. It's written in plain English — no formulas — so you can tune your size charts, fit settings, and priorities with confidence.
Three things in, one recommendation out
Every recommendation is the result of mixing what you configured for the garment with the body measurements the shopper typed in.
Your four levers
These are the only inputs you set as a merchant. Once they're configured, the same logic runs for every shopper.
① Size chart
② Fit ease
③ Fabric stretch
④ Measurement priorities
Fit ease at a glance
Fit ease is the most important dial. It tells SmartSize whether the cut is tight, regular, or roomy by design — so it knows how to interpret the chart's min/max numbers.
Priority weights — how it works
You assign each measurement a priority: NONE, LOW, NORMAL, or HIGH. Those become weights of 0 / 1 / 2 / 3 and are scaled to add up to 100%.
Example — a tailored shirt: bust HIGH, waist NORMAL, hips LOW, inseam NONE.
Where does the shopper's number land?
For each size, SmartSize takes one measurement at a time and asks: "where on the spectrum does the shopper's number fall, relative to this size's min and max?"
Imagine the size's range as a green zone in the middle, with progressively worse zones on either side:
Two important asymmetries
- Loose forgiveness depends on fit ease. A roomy garment is allowed to sit looser on the body before it starts losing points. An oversized hoodie won't penalise a slim shopper much; a bodycon dress will.
- Tight forgiveness depends on stretch. A stretchy fabric is allowed to sit a bit over the max before it starts losing points. A non-stretch poplin won't get the same allowance.
One weighted score per size
Each measurement gets a score from the previous step. SmartSize then averages them using the priority weights you set, producing one final score per size.
Example — same tailored shirt setup as before:
| Measurement | Weight | Score for size M | Contribution |
|---|---|---|---|
| Bust (HIGH) | 50% | Perfect · 1.00 | +0.50 |
| Waist (NORMAL) | 33% | Perfect · 1.00 | +0.33 |
| Hips (LOW) | 17% | Snug · 0.40 | +0.07 |
| Total for size M | +0.90 | ||
The same calculation runs for every size in the chart. The highest total wins — unless the size has been ruled out (see §5) or there's a tie (see §6).
Disqualification (the "won't fit" gate)
A great score on bust doesn't save a size if the waist is hopelessly tight. SmartSize ejects sizes from consideration when any important measurement is too far outside the range.
The rules in plain English
- HIGH priority measurements are strictly judged. If the shopper's value is more than the tolerance over the size's max (or under the min), the size is out.
- NORMAL priority measurements get a small extra buffer — 3 cm for adults, 2 cm for kids — before they trigger disqualification.
- LOW and NONE priority measurements never disqualify a size on their own. They only nudge the score.
Garment-type extras
Picking an archetype (like skinny jeans or bodycon dress) turns on a few extra guardrails:
| Garment type | What also disqualifies a size |
|---|---|
| Bottoms (jeans, trousers) | Hip is way too tight, or waist is bigger than hip's best match. |
| One-piece (dresses, swimwear) | Any critical girth (bust, waist, or hip) is too tight, even by a smaller margin. |
| Tops, outerwear, general | No extra rules — just the standard ones above. |
The highest score wins — usually
Among the sizes that survived disqualification, the one with the highest total wins. When two are basically tied (within 0.15 points), we have to pick a direction.
| Customer type | Tie-break direction | Why |
|---|---|---|
| Adults (man, woman, unisex) | Larger size | Easier to alter down than up; more comfortable to wear. |
| Children (boy, girl) | Always larger | Kids grow; sleeves can be rolled. |
| Adults in compression/slim + stretchy garments | Smaller size | That's the design intent — bandage dresses, leggings, swimwear hug the body. |
What "tied" really means
"Tied" here means the two top sizes scored within 0.15 points of each other on the −1.0-to-+1.0 scale. Anything bigger than that and we just pick the higher score outright.
When the rules bend
Three situations get bespoke treatment. They're worth understanding because they explain why two shoppers with the same numbers may get different sizes.
Kids: growth bias
For boys and girls, the next-larger size gets a small bonus (about 20% of the score scale, dialled down for narrow charts). If a slightly larger size is otherwise close in score, it wins. Sleeves get rolled; jeans get hemmed.
Slim + stretchy
When the garment is cut slim or compression and the fabric is stretchy, tied scores go to the smaller size. This is the design intent for bodycon dresses, sports bras, swim one-pieces, and leggings. You'll see a special shopper banner explaining this.
Pets: pass/fail
For dogs and cats, no scoring or weighted averages. Each measurement either falls inside a size's range or it doesn't. If every measurement agrees on a size, we recommend it; if they disagree wildly, we say so instead of guessing.
Two labels you'll see in the popup
Every recommendation comes with a confidence rating (how clear the data was) and a strength rating (how well the size actually fits). They are independent — high confidence in a so-so size is possible.
Confidence
How well the shopper's measurements agreed on one size.
| high | Every measurement points at the same size. |
| medium | Measurements split across two adjacent sizes. |
| low | Measurements span 3+ sizes or some are missing. |
Strength
How well the chosen size actually fits the shopper.
| strong | Everything falls inside the chart. |
| moderate | Slightly off-chart, on the loose side. |
| cautious | Off-chart with at least one tight area. |
| speculative | Way off-chart, or no size really fits. |
Maria orders a tailored shirt
Putting it all together with a single, end-to-end story.
Setup
Garment: tailored shirt · Fit: +9 cm (Fitted) · Stretch: 0 cm (Non-stretch) · Priorities: Bust HIGH, Waist NORMAL, Hips LOW, Inseam NONE.
| Size | Bust (cm) | Waist (cm) | Hips (cm) |
|---|---|---|---|
| S | 82 – 86 | 64 – 68 | 90 – 94 |
| M | 86 – 90 | 68 – 72 | 94 – 98 |
| L | 90 – 94 | 72 – 76 | 98 – 102 |
Maria's measurements: bust 88, waist 70, hips 96.
Compute priority weights. Bust HIGH(3) + Waist NORMAL(2) + Hips LOW(1) + Inseam NONE(0) = 6. So bust = 50%, waist = 33%, hips = 17%, inseam ignored.
Score each size. Maria's numbers slot neatly into M's ranges, so every measurement is a perfect fit for M. For S, every measurement is over the max — way too tight.
| Size | Bust 88 | Waist 70 | Hips 96 | Total |
|---|---|---|---|---|
| S | Too tight | Too tight | Too tight | −1.43 |
| M | Perfect | Perfect | Perfect | +1.00 |
| L | Relaxed | Relaxed | Relaxed | −0.18 |
Check disqualifications. Size S fails because Maria's bust (HIGH priority) is 2 cm over the max, with zero stretch and zero fit tolerance to absorb it. S disqualified
Pick the winner. M's score of +1.00 beats L's −0.18 by far more than 0.15 — no tie-break needed. M wins
Set confidence & strength. All three measurements landed in M's ranges, so: confidence: high strength: strong
The shopper sees: "We recommend M — fits comfortably."
A trickier case — Maria's stretchy bodycon dress
Same Maria (bust 88, waist 70, hips 96), but now shopping for a bodycon dress cut at +5 cm with moderate stretch (7 cm). The dress is rated bust HIGH, waist HIGH, hips HIGH.
- The 7 cm of stretch and slim cut activates the slim+stretchy rule: tied sizes go to the smaller one.
- If Maria scores roughly the same on size M and L, the smaller (M) wins — that's the design intent of a body-hugging dress.
- The shopper sees a banner: "Bodycon dresses are designed to hug — we picked the smaller of two close matches."