General Synonyms:
* Measurement
* Quantification
* Numerical observation
* Empirical measurement
* Data collection
* Statistical analysis
* Objective observation
More specific synonyms:
* Counting
* Weighing
* Measuring length/width/height
* Determining volume/mass
* Assessing temperature/pressure
* Analyzing chemical composition
* Calculating rate/frequency/density
Note: "Quantitative observation" emphasizes the use of numbers and measurements. Some synonyms, like "data collection" and "statistical analysis," encompass a broader scope that may involve both qualitative and quantitative data.
The most appropriate synonym will depend on the specific context in which you are using it.