Definition
The number written below the line in a fraction. It indicates how many equal parts the whole has been divided into, while the number above the line (the numerator) indicates how many of those parts are being counted.
Plain English
The bottom number of a fraction. It tells you how many equal pieces the whole was cut into.
Context Anchor
Seen in aviation maintenance math when working with fractions, measurements, and calculation steps.
Derivation
From the Latin denominare, meaning 'to name.' The denominator 'names' the size of the parts — halves, quarters, sixteenths — so you know what kind of pieces you are working with.
Why Pilots Care
Aircraft maintenance routinely uses fractional measurements (e.g., 3/16 inch, 7/8 inch). Misreading the denominator means picking the wrong drill bit, wrench, or shim — which can lead to incorrect fits, damaged parts, or unsafe assemblies.
Analogy
If a pizza is cut into 8 equal slices, 8 is the denominator. It tells you the whole pizza was divided into eight equal parts.
Intuition Check
Do not read the denominator as the amount you have. It tells how many equal parts make one whole; the top number tells how many of those parts are being counted.
Example Sentence 1
When reading 5/16 on the drill chart, the denominator 16 tells the technician the inch is divided into sixteen equal parts.
Example Sentence 2
In the formula for percentage wear on a component, the original thickness serves as the denominator.