A 25mm TMT bar weighs 3.853 kg per metre, calculated with the d²/162.2 formula: (25 × 25) ÷ 162.2 = 3.853 kg/m.
A standard 12 m length of 25mm TMT weighs 46.24 kg (3.853 kg/m × 12 m).
Approximately 21 standard 12 m bars of 25mm TMT make one tonne (1,000 ÷ 46.24 kg per bar). Actual counts vary with rolling tolerance under IS 1786.