Calculator Tools
Rule of Three
Scale a value proportionally when you know the ratio. Useful for recipes (double an ingredient), maps (convert distances), currency (apply an exchange rate), or any situation where two things grow at the same rate.
A1
B1
A2
B2
A1 / B1 = A2 / B2 → B2 = ( B1 × A2 ) / A1
Percentage
X% of Y — find a portion of a number (tax, tip, commission). What % — figure out how big a slice something is (score out of total, share of a budget). % change — measure growth or reduction between two values (price increase, weight loss, traffic change).
% of =
is % of
from to = %