| Pen Twyn Glas | |
| Elevation M: | 646 |
| Prominence M: | 21 |
| Parent Peak: | Pen Allt-mawr |
| Listing: | sub Hewitt, Nuttall |
| Language: | Welsh |
| Location: | Black Mountains, South Wales |
| Grid Ref Uk: | SO215300 |
| Topo: | OS Landranger 161 |
Pen Twyn Glas is a top of Pen Allt-mawr in the Black Mountains in south-eastern Wales. It lies in between Pen Allt-mawr and Mynydd Llysiau.
The summit is merely a grassy bump on the ridge marked by a pile of stones.[1]