A 10mm TMT bar weighs 0.617 kg per metre, calculated with the d²/162.2 formula: (10 × 10) ÷ 162.2 = 0.617 kg/m.
A standard 12 m length of 10mm TMT weighs 7.40 kg (0.617 kg/m × 12 m).
Approximately 135 standard 12 m bars of 10mm TMT make one tonne (1,000 ÷ 7.40 kg per bar). Actual counts vary with rolling tolerance under IS 1786.