While the "Scale Down" version converts linear measurements of real-world objects to a smaller scale, this one lets you check the real-world size of a scale replica. It can also be used in scale-to-scale conversions (see below).
These calculators are pretty simple since all they do is multiply and divide. The "Scale Down" calculator is useful for modeling from 1:1 objects since you can put in the actual 1:1 size measurement of an object in inches (as they're frequently provided), and it will output the scaled size in metric, which is easier to work with. You'll still have to do any preliminary feet-to-inches conversions yourself unless you enter the numbers in the spreadsheet-like syntax, shown below.
Because it evaluates the expression you enter, you can enter something like (5*12)+4+(3/4), which is like saying "five feet four and three-quarter inches" (5 feet times 12 inches plus 4 inches plus 3/4 of an inch).