In Syracuse, New York, a student named Charles Brannock, whose father had co-founded a shoe store there in 1906, patented a foot-measuring device in 1926 and 1927 and built a company to make it. Before that, the available option was a primitive block of measured wood. Designer shoe sizing is still part measurement, part house opinion.

Here is the opinion part. European sizes run on the Paris point, two-thirds of a centimeter, and Italy and France use the same Continental scale, so a French 38 and an Italian 38 are the same length. The half sizes you see on luxury shoes were never in that original scale; they are a maker's interpolation. And the number describes the last, not your foot. Every house builds around its own last, which is why a loafer and a sharp pump with the same 38 inside can feel like two different shoes.

So read loafers line by line. The Row's Casa leather loafers in black say true to size, with half sizes taking the next size up, and the Soft suede loafers in brown simply say true to size. Saint Laurent's Le Loafer Cassandre in black also says true to size, on an elongated Italian last with a narrow waist. Khaite's Jane moccasins in beige say true to size too. Then the Gucci Jordaan pair split: the black leather says fits large, take a half size smaller, while the beige suede says fits small, take a half size larger. Same name, opposite advice. The Georgie from Gianvito Rossi says take your normal size.

My tip for October, when you are back in real socks: measure both feet at the end of the day, standing on a hard floor, and use the larger one. Then write the page's fit line next to the number before you order.

Louboutin's own fit page makes one point that fixes half the sizing mistakes I see: going up in size only changes the length. It does not widen the toe box. The Sweetie Jane ribbon-detailed patent flats in black are listed as true to size, so your normal number is the place to begin there.

Flats are where the notes fan out. The Petal Anagram flats from Loewe in red fit small, and the page suggests a full size larger. The BB suede flats from Manolo Blahnik in brown and the Luna flats from Le Monde Beryl in red both fit slightly small, with a half size larger recommended. Go the other way for the Ellie suede flats from Aeyde in burgundy, which fit slightly large and suggest a half size smaller. The Carla raffia Mary Janes from Gianvito Rossi in tan say take your normal size. Khaite's Marlene in snake print says true to size, and the label's own page for the Marlene says take your normal size. Alaïa's red mesh flats say true to size, then split by foot: narrow feet try a half size smaller, wide feet a half size up.

Other labels are just as blunt. A Miu Miu ballerina page reads Runs small; order 1/2 size up, and a Mansur Gavriel Dream Ballerina note says Runs small: We recommend going up a half size. Neither is in this edit, but they show how a flat can read.

My fitting-room test: stand, then lift your heel. A flat that slips off is too long. What I would skip: ordering a full size up for a tight toe, since that only adds length.

Boots make the last matter most, because there is nowhere for a tight forefoot to hide. Saint Laurent's ankle boots sit on those elongated Italian lasts, and ankle boots from the label usually fit slimmer than average across the forefoot. The Niki Cassandre-embellished boots in brown say true to size and point you to the brand's size guide.

The Row's zipped leather ankle boots in black say take your normal size. So do Jimmy Choo's Frankie 85 suede boots in chocolate and Gianvito Rossi's Levy 55 in burgundy, which says true to size. Khaite's Clive suede knee boots in brown are true to size, and half sizes take the next size up. Alaïa's Tube 100 grosgrain-trimmed tulle knee boots in black and Toteme's Contour ankle boots in black are true to size, but half sizes take the next size down. Opposite half-size advice, same word true. Gucci's Savoy canvas-jacquard knee boots in beige fit small and suggest one size larger.

Pair a knee boot with a short skirt and tights now that it is cold, and test it in the exact tights you will wear. Zip the shaft all the way, then sit and bend the knee. For the ankle boots, take a few steps and watch whether the heel lifts.

What I would skip: a boot a size up on a hunch about socks. Use a thicker sock in the fitting room and decide there.

Two pumps labelled 38 can feel entirely different, because one sits on a sharply pointed last and the other on a rounded toe box. That is the whole story with heels. The Manolo Blahnik Maysli 70 buckled slingbacks in burgundy fit slightly small, and a half size larger is suggested. Aquazzura's Orbit 65 bouclé pumps in cream say the same.

Then the large ones. The Gianvito Rossi 95 crepe-satin pumps in brown fit large, and the page recommends one size smaller. Alaïa's Vienne 100 laser-cut suede pumps in black are true to size, with half sizes taking the next size down. Saint Laurent's Goya 95 crepe slingbacks in brown, Toteme's 55 leather slingbacks in black, Christian Louboutin's Dolly 100 patent pumps in red and Khaite's Colleen 75 in black all say true to size. Louboutin says its shoes generally run true to size, but that everyone can have a different fitting.

For slingbacks, check the strap in the fitting room: it should hold the heel without a gap when you walk, not just when you stand. For a patent pump like the Dolly, remember that Louboutin says most materials will stretch and form to the foot after multiple wears, so a pair that is snug but not painful has room to settle.

What I would skip: sizing a pointed pump up a whole number to cure a pinch. The length goes, the pinch stays.

Read the half-size line in the sneaker notes, not just the headline. The EU step is 6.67 mm, while UK and US sizes use the barleycorn at 8.47 mm, so the two scales never line up neatly and the brand has to round. Brannock's old chart says each additional US size is a third of an inch longer.

Golden Goose's Super Star leather sneakers in burgundy and the Soul-Star suede sneakers in red both say true to size, half sizes take the next size up. Loewe's Ballet Runner 2.0 in burgundy says the same. Toteme's Flex leather sneakers in beige are true to size but ask for the next size down at half sizes. The Boxe leather sneakers from McQueen in black fit large, with one size smaller recommended. Gucci's Ace 2.0 in white and Jimmy Choo's Diamond Light Flex lace-ups in dark brown say true to size, and Isabel Marant's Beth in white says true to size with a note to see the brand guide.

I would wear the Ace with a wide-leg jean and a camel coat, and lace the Boxe snugly with a thick sock. Test them standing, then take a few steps to see whether your heel lifts out.

What I would skip: matching your running-shoe size without checking the page. Different makers, different lasts.

Brannock beat the wooden block with a better tool, and I would start with a simpler one: a sheet of paper, a pencil, a ruler and the end of the day. Measure both feet, use the larger, and convert to the brand's own chart.

Then read the fit line on the exact shoe. Sam Edelman says most of its styles fit true to size, but to check the chart and reviews for narrow, small or large. Rabanne shoes follow standard EU sizing, and Toga says its sizes may vary by product. Order the number the page gives you, and take the half size it names, not the one you guess.