The objective of this study was to compare the precision of CH₄ estimates using calculated CO_{2 (HP)} by the CO₂ method (CO₂T) and measured CO₂ in the respiration chamber (CO₂R). The CO₂R and CO₂T study was conducted as a 3 × 3 Latin square design where 3 Dexter heifers were allocated to metabolic cages for 3 periods. Each period consisted of 2 weeks of adaptation followed by 1 week of measurement with the CO₂R and CO₂T. The average body weight of the heifer was 226 ± 11 kg (means ± SD). They were fed a total mixed ration, twice daily, with 1 of 3 supplements: wheat (W), molasses (M), or molasses mixed with sodium bicarbonate (Mbic). The dry mater intake (DMI; kg/day) was significantly greater (P < 0.001) in the metabolic cage compared with that in the respiration chamber. The daily CH₄ (L/day) emission was strongly correlated (r = 0.78) between CO₂T and CO₂R. The daily CH₄ (L/kg DMI) emission by the CO₂T was in the same magnitude as by the CO₂R. The measured CO₂ (L/day) production in the respiration chamber was not different (P = 0.39) from the calculated CO₂ production using the CO₂T. This result concludes a reasonable accuracy and precision of CH₄ estimation by the CO₂T compared with the CO₂R.