The metric system was officially introduced by a law passed on 17 December 1923. However, old Thai units are still in common use, especially for measurements of land which is often quoted using the traditional Thai system of wha, ngaan and rai. In the provinces, old-times will occasionally use the traditional Thai system of weights and measurements. Here are some conversions:
| Thai system | Metric System |
| 1 square wha | 4 square meters |
| 1 ngan (100 square wha) | 400 square meters |
| 1 rai (4 ngan) (1 sq cen) | 1600 square meters |
| 1 baht | 15.16 grams |
| 1 tamlung (4 Baht) | 60 grams |
| 1 chang (20 tamlung) | 1.2 kg |
| 1 haap (50 chang) | 60 kg |
| 1 niu | 2 cm |
| 1 kheup (12 niu) | 25 cm |
| 1 sawk (2 kheup) | 50 cm |
| 1 waa (4 sawk) | 2 meters |
| 1 sen (20 waa) | 40 meters |
| 1 yoht (400 sen) | 16 km |
| 1 kwien | 2,000 liters |
| 1 ban | 1,000 liters (2 ban=1 kwien) |
| 1 sat | 20 liters (50 sat=1 ban) |
| 1 tannan | 1 liter (20 tannan=1 sat) |
