How datfit predicts your size.

datfit gives you one size and a match score — not a table to puzzle over. Two engines power it, depending on what chart is available.

1. Store & standard charts: body estimation

Store widgets and the “Any brand” option use body-measurement charts (chest or bust, waist, hips — in cm). Because shoppers rarely know those numbers, datfit estimates them from height, weight and BMI using regressions calibrated against common retail charts, separately for women and men. Body shape (slim, athletic, curvy, fuller) shifts individual measurements by a few centimetres, and waist estimates grow slightly after age 40.

2. Matching and scoring

For every size row, each measurement is compared with the row's range. The distance from the range centre is normalised by the range's half-width d:

• Inside the range (|d| ≤ 1) the penalty is d² — gentle.
• Outside it the penalty is 1 + 4·(|d| − 1) — steep, so sizes that contain you win.
• Chest/bust carries full weight, waist 0.85 and hips 0.8.

Fit preference adds ease before scoring: fitted −2 cm, relaxed +4 cm. If you tell us your usual size, rows away from it get an extra penalty of 1.6 × (steps away)², because a size you actually wear is stronger evidence than a BMI estimate. When the runner-up is an adjacent size with a close score, datfit shows it as the “between sizes” alternative.

3. Brand charts: containment-first

Brand charts in the free size finder publish height and weight ranges. Each size gets outside × 5 + midpoint × 0.1, where outside is how far you fall outside the ranges and midpoint is distance from their centre. The 5× weight means any size that fully contains you beats one that doesn't. Body shape and fit preference then move the pick one size only when that neighbour scores within 0.8; a usual size within 1.2 wins ties.

4. Shoes

Your usual EU size becomes a foot length using the Paris-point relation foot ≈ EU ÷ 1.5 − 1.5 cm, then it is matched to the chart's foot-length ranges. Stores can mark their shoes as running small or large, which shifts the foot length by one size (≈0.66 cm).

5. Confidence

The match score combines how well the best size fits (e^(−score)), how clearly it beats the runner-up, and whether it agrees with your usual size. It is clamped between 51% and 97% — no chart-based prediction deserves 100%.

6. Selecting the size on a store

The widget recognises dropdowns, radio groups and size buttons, and normalises labels so “Medium”, “M”, “وسط” and “EU 42.0” line up with your recommendation before it selects the size for you.

Limitations

Estimates from height and weight can't see everything — adding your usual size or a store's own measurements improves accuracy. Garments with unusual cuts, stretch or oversized styling may fit differently from their chart.

Last updated: 15 September 2026.