Nant-ddu is located in the county of Powys, Wales, six miles north-west of the town of Merthyr Tydfil, 25 miles north-west of the major city of Newport, 27 miles north-west of Cardiff, and 144 miles west of London. Nant-ddu lies just north of the Mid Glamorgan border, and was historically in the county of Brecknockshire. Nant-ddu falls within the unitary authority of Powys - Powys. It is in the CF48 postcode district. The post town for Nant-ddu is Merthyr Tydfil.


Nant-ddu is in the ceremonial county of Powys, the historic county of Brecknockshire, and the administrative county of Powys - Powys.
| Ceremonial County | Powys |
|---|---|
| Historic County | Brecknockshire |
| Administrative County | Powys - Powys |
Nant-ddu is situated towards the southernmost extremity of Powys, and roughly centrally between the easternmost and westernmost extremities of Powys.

The nearest postcode to the centre of Nant-ddu is CF48 2HY.
Nant-ddu is situated towards the northernmost extremity of the CF48 postcode district, and towards the westernmost extremity of the CF48 postcode district.

The post town for Nant-ddu is Merthyr Tydfil. Nant-ddu is in the CF48 postcode district, which corresponds to the post town of Merthyr Tydfil.
The centre of Nant-ddu is located at position 51.82466° latitude and -3.4476° longitude.
| Latitude | 51.82466° |
|---|---|
| Longitude | -3.4476° |
The centre of Nant-ddu is located at the grid reference easting 300330 and northing 214995 within the British National Grid (OSGB36) system.
| Easting | 300330 |
|---|---|
| Northing | 214995 |
Position of Nant-ddu relative to nearby towns. Distance is measured from the centre of Nant-ddu to the centre of the town.
Position of Nant-ddu relative to nearby cities. Distance is measured from the centre of Nant-ddu to the centre of the city.