"mean amount" is correct and usable in written English.
You can use it to refer to an amount that is calculated by taking the average of a set of numbers. For example, "The mean amount of rainfall in August was 4 inches."
The mean amount of tissue at the 6 o'clock position significantly changed over time (P <.01).
It measures the mean amount of data (in kilo bytes) that each MN generates or forwards.
The mean amount of setback at point B was 5.05 ± 2.84 mm (Table 1).
The mean amount of setback was 4.3 mm after 1.5 years from surgery.
The mean amount of correction in the 1.DMAA at the early postoperative stage was 5.6°.
The mean amount of wild foods obtained by households was 156.61 kg per household per annum.
Thus the mean amount of narcotic analgesic administered was significantly less in patients treated with indomethacin rectal suppositories.
The mean amount of abnormal uterine bleeding was reduced at 6 months compared to immediately prior to treatment (P=0.0001).
The analysis showed that the PWM values have a significant effect on the mean amount of thrust.
Philosophy departments differ enormously in the amount of discretionary funds available to them, with the mean amount extremely low.
With each injection campaign the mean amount of seepage water was lowered, though the gain of each campaign decreased.
