Definition
To estimate a value that falls between two known values in a table or chart by calculating proportionally between them. In aviation performance work, interpolation is used when the actual conditions (temperature, weight, altitude) sit between the values listed in a performance table.
Plain English
When the number you need isn't shown in the table but the numbers just above and just below it are, you work out roughly where your number would sit between them.
Context Anchor
Seen when using aircraft performance tables, such as takeoff distance or landing distance tables, when the exact condition is not listed.
Derivation
From Latin 'inter' (between) and 'polire' (to polish or smooth). Originally meant to insert something between existing things to smooth them out. In math and aviation it means filling in the gap between two known points.
Why Pilots Care
Correct interpolation gives accurate performance numbers for takeoff, climb, or landing instead of forcing the use of the nearest listed value.
Analogy
If a ruler shows 4 inches and 5 inches, and a mark is halfway between them, you would call it about 4.5 inches. Interpolation does that same kind of in-between estimate with table numbers.
Grounding Statement
Picture a chart row for 2,000 feet and another for 3,000 feet; interpolation lets you locate the exact point at 2,500 feet without guessing.
Intuition Check
Interpolate does not mean make a random guess. It also does not mean automatically use the closest listed number; it means estimate the value between the surrounding numbers.
Example Sentence 1
The takeoff distance table showed values for 2,500 lb and 3,000 lb, so she interpolated to find the distance for her actual weight of 2,750 lb.
Example Sentence 2
When the outside air temperature fell between two listed values, she interpolated to determine the correct density altitude.