A good rule of thumb is to keep within 5mm.
Magnum condom size. 6 rows trojan™ and magnum™ condom size charts. Girthwise, 5.3” or so should be plenty to wear a magnum snugly. Technically speaking, magnum condoms are wider or have bigger girth than regular condoms.
At 6” girth, i find magnum xls to be pretty damn tight (they seem designed more for ~5.6” girth). Based on the text, a trojan magnum condom should fit snugly between men’s 8.07 inches and 9.5 inches in length, 2.13 inches and 2.36 inches in width, and between 8.07 inches. It is about 15% bigger in girth (just more or less 1 cm) than regular condoms.
Condoms should be tighter at the base so they don’t slip off, and whether you like a roomier condom or a tighter condom along the shaft and head is up to you. 37 rows condom size by the base flat width: Magnums are available in several varieties like original, ribbed.
According to condom depot, magnums measure 8.12 inches long with a width of 2.12 inches.