Shirt sizing questions answered, in plain sentences

These pages answer the sizing questions people ask in whole sentences, using published garment measurements rather than opinion. Start with the question that sounds like yours, and each page gives the answer first and the numbers behind it second.

What kind of questions belong here?

The ones people type as sentences rather than keywords. Every page in this section opens with the answer, then shows the garment measurements it rests on. Where a figure is uncertain, the page says so instead of rounding it into confidence.

If you would rather start from a chart or a tape measure, the size charts and the measuring guides cover the same ground in a different shape.

Which answer do you need?

What size am I in a different brand?Carry one shirt you already like across to a brand you have never worn, using flat chest measurements. Why does my size change between stores?What a letter actually names, and why two Mediums can be three inches apart. How do I stop returning clothes?The checks that catch a bad fit before the order, not after the parcel arrives. How do I find more shirts like one I own?Measure the shirt that works, then search on its numbers rather than its label. What shoes are these?Reference reading on identifying a shoe and where a photograph stops being enough. Does Nike run small?How to test a "runs small" claim against published measurements instead of reviews.

Why do sizes disagree in the first place?

Because a letter names a garment, not a body. A ladies' Gildan G500L Medium publishes a 17.5" chest measured flat. The unisex Mediums in the same set publish 20.0" to 20.5". That is a three inch gap on the same letter, and it repeats at Large. Neither shirt is mislabelled. The letter is simply doing no work, which is the subject of vanity sizing.

Do these answers cover shoes and sunglasses too?

Partly. ShirtMath scans shirts laid flat, not feet or frames. The shoe and eyewear pages are reference reading: they explain how to measure and how to read the numbers printed on a frame. A photograph alone cannot tell you your shoe size, because that needs your known size or a foot measurement.