1. An Approximation is a rough estimate or guess at something

2. A rough estimate of the costs of employee and manager time spent on administration is $2.3B per year.

3. A Crude [=rough] estimate She first described the procedure in Crude terms, and then went into more detail

4. ‘The brightness and density of mito-GFP labeling within presynaptic boutons provides a rough estimate for mitochondrial concentration in the presynaptic Axoplasm.’

5. Ballpark (third-person singular simple present Ballparks, present participle Ballparking, simple past and past participle Ballparked) To make a rough estimate of