25. 1 km. According to Baidu map, the distance from China Institute of Metrology to Beijing Tiantan Hospital is 25. 1 km.

1. First walk 280 meters from China Institute of Metrology to Heping Xiqiao Station, and take Metro Line 5 and get off at Songjiazhuang.

2. Secondly, take the subway 10 line from Songjiazhuang Station and get off at Shoujingmao Station.

3. Finally, walk 1.3km from Shoujingmao Station to Beijing Tiantan Hospital.