Size 10/12 is a youth medium in Port & Company PC54Y and size 10/12 is a youth medium in Gildan 8800B, and a PC54Y youth medium measures 17 inches across the chest laid flat against 18 inches for an adult small in the matching PC54.
Method: compiled 2026-09-29 from 11 sources, each named beside its row: Port & Company PC54Y youth spec sheet (https://www.sanmar.com/p/3986_Purple/specSheetMeasurements, fetched live 2026-09-29); Gildan 8800B youth polo spec sheet (https://www.sanmar.com/p/5323_Royal/specSheetMeasurements, fetched live 2026-09-29); Port & Company PC54 spec sheet (https://www.sanmar.com/p/3985_AquaticBl/specSheetMeasurements, fetched live 2026-09-29); Bella+Canvas youth chart (https://www.bellacanvas.com/fit-size-charts, fetched live 2026-09-29); Gildan 5000B youth spec sheet (https://www.sanmar.com/p/439_Daisy/specSheetMeasurements, fetched live 2026-09-29); our page https://theloyalbrand.com/blogs/blog/youth-medium-vs-adult-small-a-complete-size-guide (read 2026-09-29); our page https://theloyalbrand.com/blogs/blog/bella-canvas-youth-sizing-guide (read 2026-09-29); our page https://theloyalbrand.com/blogs/blog/comfort-colors-youth-sizing-guide (read 2026-09-29); Port Authority K500 polo spec sheet (https://www.sanmar.com/p/1225_Red/specSheetMeasurements, fetched live 2026-09-29); Gildan 5000 spec sheet (https://www.sanmar.com/p/625_Black/specSheetMeasurements, fetched live 2026-09-29); Port & Company PC61 spec sheet (https://www.sanmar.com/p/1634_Ash/specSheetMeasurements, fetched live 2026-09-29). Where a source gives inches only, cm is converted at 2.54 cm per inch and rounded to the nearest cm. Values a source publishes outside a plausible garment range are left out.
Which youth size is 10/12?
Youth shirts carry a letter and a number pair; the spec sheets print both.
| Size | Brand and style | Numeric size | Source |
|---|---|---|---|
| Youth XS | Port & Company PC54Y youth | 4/5 | www.sanmar.com/p/3986_Purple/specSheetMeasurements, 'Size' row, fetched 2026-09-29 |
| Youth S | Bella+Canvas youth | 6/8 | bellacanvas.com/fit-size-charts, "Youth" row, fetched 2026-09-29 |
| Youth S | Gildan 8800B youth polo | 6/8 | www.sanmar.com/p/5323_Royal/specSheetMeasurements, 'Size' row, fetched 2026-09-29 |
| Youth S | Port & Company PC54Y youth | 6/8 | www.sanmar.com/p/3986_Purple/specSheetMeasurements, 'Size' row, fetched 2026-09-29 |
| Youth M | Bella+Canvas youth | 10/12 | bellacanvas.com/fit-size-charts, "Youth" row, fetched 2026-09-29 |
| Youth M | Gildan 8800B youth polo | 10/12 | www.sanmar.com/p/5323_Royal/specSheetMeasurements, 'Size' row, fetched 2026-09-29 |
| Youth M | Port & Company PC54Y youth | 10/12 | www.sanmar.com/p/3986_Purple/specSheetMeasurements, 'Size' row, fetched 2026-09-29 |
| Youth L | Bella+Canvas youth | 14/16 | bellacanvas.com/fit-size-charts, "Youth" row, fetched 2026-09-29 |
| Youth L | Gildan 8800B youth polo | 14/16 | www.sanmar.com/p/5323_Royal/specSheetMeasurements, 'Size' row, fetched 2026-09-29 |
| Youth L | Port & Company PC54Y youth | 14/16 | www.sanmar.com/p/3986_Purple/specSheetMeasurements, 'Size' row, fetched 2026-09-29 |
| Youth XL | Bella+Canvas youth | 18/20 | bellacanvas.com/fit-size-charts, "Youth" row, fetched 2026-09-29 |
| Youth XL | Gildan 8800B youth polo | 18/20 | www.sanmar.com/p/5323_Royal/specSheetMeasurements, 'Size' row, fetched 2026-09-29 |
| Youth XL | Port & Company PC54Y youth | 18/20 | www.sanmar.com/p/3986_Purple/specSheetMeasurements, 'Size' row, fetched 2026-09-29 |
How big is a youth 10/12 across the chest?
Youth medium, laid flat and by the body chest it fits.
| Size | Brand and style | Measurement | Inches | cm | Source |
|---|---|---|---|---|---|
| Youth M | Gildan 5000B youth | Chest, laid flat | 18 | 46 (converted) | www.sanmar.com/p/439_Daisy/specSheetMeasurements, Product Measurements 'Chest' row, fetched 2026-09-29 |
| Youth M | Gildan 8800B youth polo | Chest, laid flat | 17 | 43 (converted) | www.sanmar.com/p/5323_Royal/specSheetMeasurements, Product Measurements 'Chest' row, fetched 2026-09-29 |
| Youth M | Port & Company PC54Y youth | Chest, laid flat | 17 | 43 (converted) | www.sanmar.com/p/3986_Purple/specSheetMeasurements, Product Measurements 'Chest' row, fetched 2026-09-29 |
| Youth M | Bella+Canvas | Chest, laid flat | 15.25 | 39 (converted) | theloyalbrand.com/blogs/blog/youth-medium-vs-adult-small-a-complete-size-guide, table "Bella+Canvas (Style 3001Y Youth / 3001 Adult)", row "Youth Medium (YM)", read 2026-09-29 |
| Youth M | Gildan 5000B youth | Body chest it fits | 27.5-28.5 | 70-72 (converted) | www.sanmar.com/p/439_Daisy/specSheetMeasurements, Size Chart 'Chest Width' row, fetched 2026-09-29 |
| Youth M | Port & Company PC54Y youth | Body chest it fits | 28-30 | 71-76 (converted) | www.sanmar.com/p/3986_Purple/specSheetMeasurements, Size Chart 'Chest' row, fetched 2026-09-29 |
| Youth M | Bella+Canvas | Body chest it fits | 28-30 | 71-76 (as published) | theloyalbrand.com/blogs/blog/bella-canvas-youth-sizing-guide, table "Bella+Canvas Youth Size Chart", row "YM", read 2026-09-29 |
| Youth M | Comfort Colors | Body chest it fits | 30-32 | 76-81 (as published) | theloyalbrand.com/blogs/blog/comfort-colors-youth-sizing-guide, table "Comfort Colors Youth Size Chart: Every Size", row "YM", read 2026-09-29 |
How does it compare with adult XS and S?
The smallest adult sizes, measured the same way.
| Size | Brand and style | Measurement | Inches | cm | Source |
|---|---|---|---|---|---|
| Adult XS | Port Authority K500 polo | Chest, laid flat | 19.5 | 50 (converted) | www.sanmar.com/p/1225_Red/specSheetMeasurements, Product Measurements 'Chest' row, fetched 2026-09-29 |
| Adult XS | Port Authority K500 polo | Body chest it fits | 32-34 | 81-86 (converted) | www.sanmar.com/p/1225_Red/specSheetMeasurements, Size Chart 'Chest' row, fetched 2026-09-29 |
| Adult S | Gildan 5000 | Chest, laid flat | 18 | 46 (converted) | www.sanmar.com/p/625_Black/specSheetMeasurements, Product Measurements 'Chest' row, fetched 2026-09-29 |
| Adult S | Port & Company PC54 | Chest, laid flat | 18 | 46 (converted) | www.sanmar.com/p/3985_AquaticBl/specSheetMeasurements, Product Measurements 'Chest' row, fetched 2026-09-29 |
| Adult S | Port & Company PC61 | Chest, laid flat | 18 | 46 (converted) | www.sanmar.com/p/1634_Ash/specSheetMeasurements, Product Measurements 'Chest' row, fetched 2026-09-29 |
| Adult S | Port Authority K500 polo | Chest, laid flat | 20.5 | 52 (converted) | www.sanmar.com/p/1225_Red/specSheetMeasurements, Product Measurements 'Chest' row, fetched 2026-09-29 |
| Adult S | Gildan 5000 | Body chest it fits | 36-37 | 91-94 (converted) | www.sanmar.com/p/625_Black/specSheetMeasurements, Size Chart 'Chest' row, fetched 2026-09-29 |
| Adult S | Port & Company PC54 | Body chest it fits | 35-37 | 89-94 (converted) | www.sanmar.com/p/3985_AquaticBl/specSheetMeasurements, Size Chart 'Chest' row, fetched 2026-09-29 |
| Adult S | Port & Company PC61 | Body chest it fits | 35-37 | 89-94 (converted) | www.sanmar.com/p/1634_Ash/specSheetMeasurements, Size Chart 'Chest' row, fetched 2026-09-29 |
| Adult S | Port Authority K500 polo | Body chest it fits | 35-37 | 89-94 (converted) | www.sanmar.com/p/1225_Red/specSheetMeasurements, Size Chart 'Chest' row, fetched 2026-09-29 |
What about 14/16 and 18/20?
The next two youth sizes up.
| Size | Brand and style | Measurement | Inches | cm | Source |
|---|---|---|---|---|---|
| Youth L | Gildan 5000B youth | Chest, laid flat | 19 | 48 (converted) | www.sanmar.com/p/439_Daisy/specSheetMeasurements, Product Measurements 'Chest' row, fetched 2026-09-29 |
| Youth L | Port & Company PC54Y youth | Chest, laid flat | 18 | 46 (converted) | www.sanmar.com/p/3986_Purple/specSheetMeasurements, Product Measurements 'Chest' row, fetched 2026-09-29 |
| Youth XL | Gildan 5000B youth | Chest, laid flat | 20 | 51 (converted) | www.sanmar.com/p/439_Daisy/specSheetMeasurements, Product Measurements 'Chest' row, fetched 2026-09-29 |
| Youth XL | Port & Company PC54Y youth | Chest, laid flat | 19 | 48 (converted) | www.sanmar.com/p/3986_Purple/specSheetMeasurements, Product Measurements 'Chest' row, fetched 2026-09-29 |