NurseSavvy Cheat SheetProcedure
Med-Math Foundations
Overview
Med-math foundations are the small moves underneath every dosage calculation: recognizing equivalent fractions, decimals and percents; estimating the likely answer; carrying full precision through the work; rounding the final result for the requested unit; and writing the number in medication-safe notation. These steps prevent a correct formula from becoming an unsafe dose through a place-value slip, premature rounding or a missed decimal point.
Interpretation
Fraction to decimal: numerator ÷ denominator Hallmark
Decimal to percent: ×100 Hallmark×100
Percent to decimal: ÷100 Hallmark÷100
mL at 1 or more: nearest tenth Hallmark0.1 mL
mL under 1: nearest hundredth Hallmark0.01 mL
gtt/min: whole number Hallmark
Tablets: nearest half only when scored Hallmark0.5 tablet
Technique
Worked example: give three eighths of a 4 mL vial
- Convert the fraction3 ÷ 8 = 0.375
- Recognize the percent0.375 × 100 = 37.5%
- Estimate the volumethree eighths is under one half, so expect under 2 mL
- Calculate with full precision0.375 × 4 mL = 1.5 mL
- Round and write safelythe amount is at least 1 mL: 1.5 mL to the nearest tenth
During — Monitoring
Keep the unrounded value until the final line Hallmark
rounding mid-chain can change a later multiplication or divisionCompare the exact answer with a simple benchmark Hallmark
one half, one quarter and powers of ten make fast anchorsCheck that the answer's magnitude fits the available form Hallmark
a routine single dose should not require dozens of tablets or a syringe larger than the ordered volumeRecalculate independently before administering a result that differs sharply from the estimate
Patient Teaching
Use the metric markings on the supplied dosing device Hallmark
Read the decimal and unit back before measuring the dose Hallmark
Clarify any label or instruction written without a leading zero or with a trailing zero
Report Nowescalate immediately
Rounding violation Hallmark
rounded mid-chain, wrote a naked decimal such as .5, or added a trailing zero such as 5.0Place-value slip Hallmark
the decimal moved one place and changed the result tenfoldUnreasonable-magnitude blindness Hallmark
the calculation produced an implausible tablet count or volume and no estimate triggered a recheckUnit mismatch Hallmark
a correct-looking number is attached to a different unit than the requested answerClinical Pearl
Estimate first, calculate second, round once at the end, and write the answer with a leading zero but never a trailing zero.