Ht: 173cm Wt: 81kg
Calories burned w/o exercise = [(9.99 x 81 kg) + (6.25 x 173 cm) – (4.92 x 20 yrs) – 161] x 1.4 = 2283 calories
Calories burned w/ exercise = 2283 calories + (400 to 700 calories) = 2683 to 2983 calories
Therefore to sustain weight, you need around 2600 calories to a little over 3000 calories. This is your daily need. This amount depends on your exercise activity and duration. For example, if you only lift weights, then you need roughly 2700 calories a day. To drop weight, then shed off a few hundred calories from you daily need. You can lose weight from just weightlifting, but it's not as efficient as doing cardio exercise.
So start off by shedding a few hundred calories for about 2-4 weeks. Then gradually increase it to 400 calories then 500 calories.