The most accurate way to size a pair of pants online is not to measure yourself. It is to measure a pair that already fits.
The reason is simple: a brand's size chart is built from the measurements of finished garments, not from body measurements. Measure your own waist and match it against the chart, and the number is almost always off.
The three numbers to write down
Lay your favorite pair flat on the floor, smoothed out, with the button fastened.
Waist. Measure straight across the waistband from edge to edge, then double it.
Hips. Measure across the widest point, usually around 20 cm below the waistband, then double it.
Length. Measure from the top edge of the waistband down to the bottom edge of the fabric, following the outside of the leg.
Keep those three numbers in your phone. You will use them every time you shop.
How to read them on a product page
Match your numbers against the size chart, not against the letters S/M/L. The same letter can mean very different measurements from one style to the next, even within a single brand.
If your numbers land between two sizes, take the larger one.
When your waist and hips fall into different sizes
Follow the hip number. A waist that runs loose is easily handled with a belt, or taken in by a tailor in minutes. Hips and thighs that run narrow cannot be added to.
Frequently Asked Questions
Which measurements do I need before buying pants online?
Four: waist, hip and thigh circumference, plus the outside length of the leg. The most accurate method is not to measure your body but to measure a pair whose fit you already like, laid flat on the floor.
What is the difference between inseam and outside length?
The inseam is measured from the crotch down to the hem. Outside length is measured from the top edge of the waistband, running down along the side seam. The KASUAL size chart uses outside length, so do not cross-compare it against an inseam figure.
Can I work out my pants size from height and weight?
To narrow it down to two letters, yes. To settle on one, no. The KASUAL conversion table runs 40 rows for bottoms and 25 for tops, and the same person can come out differently on each: 175 cm and 72 kg reads XL in pants but L in tops.
I am between two sizes. Which one should I take?
In ankle pants, take the larger one. Of 270 exchanges filed as 'customer chose the wrong size' at the KASUAL exchange desk, the direction is clear in 219 cases: 156 asked to size up and 63 asked to size down.
Why does the letter L fit differently from one style to another?
Because every style is cut from its own pattern block. The KASUAL CX notes include a customer who wore an L that fit perfectly in one style, bought an L again in another, and could not get into it. Open the chart for that line every time you switch styles, and check it against the numbers of the pair already fitting you at home.
I followed the size chart and it still does not fit. What now?
You are not alone: 189 returns state explicitly that the size chart was read and the item still did not fit. File it through the KASUAL WhatsApp CX channel if what you want is an exchange — marketplaces can usually only issue a refund.