Every glove chart in the world comes back to two numbers: how far round the palm is below the knuckles, and how long the hand is from the wrist crease to the tip of the middle finger. EN ISO 21420, the European standard for protective gloves, numbers its sizes by the first one in inches: size 8 fits a hand 203 mm (8") around, size 9 one 229 mm (9") around. The sizer above takes both from your hand at true size, then reads every sport’s chart from them.
Four measurements, one hand
The 1:1 jaw takes the flat width across the four knuckles (adults run about 69–91 mm from the 5th to the 95th percentile) and the middle finger from the crease at its base to the tip (70–87 mm). A second step adds the palm from that crease to the wrist crease, which gives the hand length EN ISO 21420 and the golf, hockey and goalkeeper charts ask for.
Circumference is the size that matters most, and a flat ruler cannot wrap round a hand. Wrap a strip of paper round the palm below the knuckles, thumb out, mark where it meets, fold it in half or in quarters and lay it on the ruler: the sizer multiplies it back.
From width to circumference without a tape
Without a strip, the sizer estimates circumference from the flat width with the ratio measured on 2,100 adult hands: metacarpal perimeter ÷ hand breadth = 2.42 for men and 2.41 for women at the 50th percentile. An 85 mm palm becomes about 206 mm around (size 8); a 75 mm women’s palm about 181 mm (size 7).
The estimate is labelled as one on the spec sheet. Hands that are thick through the palm, or thin, measure differently, so the paper strip is worth the minute it takes.
circumference ≈ flat width × 2.42 (men) or × 2.41 (women) EN size = circumference in inches
Men's, women's and youth letters
EN ISO 21420 attaches one set of letters to its numbers: 6 XS, 7 S, 8 M, 9 L, 10 XL, 11 XXL. Women’s lines are cut a letter smaller for the same hand, so a 7" hand that is S on a unisex work glove is a women’s M. Youth sizes follow hand length: Rawlings’ batting-glove chart runs Youth S at 6–6.25" to Youth XL at 6.75–7".
Brand cuts differ inside a size: when the sizer lands between two sizes, or on the edge of a band, try both.
Why the screen can be trusted
A browser does not know how big its pixels are, so the sizer starts from a table of 114 phones, tablets, laptops and monitors matched to your screen’s size and pixel ratio, an estimate good to about five percent. Laying a coin or a bank card on the glass and matching its outline replaces the estimate with a measurement good to a fraction of a percent, saved for this screen only.
Browser zoom is corrected automatically from the pixel ratio; pinch zoom is flagged, because nothing drawn is true size until it is undone.
pixels per mm = CSS px across the card ÷ 85.60 mm ID-1 card: 85.60 × 53.98 mm (ISO/IEC 7810)