How the formula works
The Desired over Have method divides the ordered dose (Desired) by the dose on hand (Have), then multiplies by the quantity the dose on hand comes in (Quantity).
D ÷ H × Q = X
Before dividing, Desired and Have must be in the same unit. If the order is in grams and the supply is in milligrams, convert first.
Example
500 mg ÷ 250 mg × 1 tablet = 2 tablets
Three ways to set it up
After each question you can view the same answer worked by Desired / Have, Dimensional Analysis, or Ratio & Proportion. They are different ways to write the problem, and they always give the same answer. Your choice is remembered on this device.
How the levels differ
- Beginner: same units, whole or simple answers.
- Intermediate: one metric conversion (g, mg, mcg).
- Advanced: conversions with decimals, scored half tablets, or a stated rounding instruction.