Or nest a trig result: { $radiansToDegrees: { $acos: "$x" } }.
Use the degree value for display, reports, or APIs.
Piece
Required?
Role
$radiansToDegrees
Yes
Radians → degrees
Expression
Yes
Number in radians (field, literal, or nested trig)
Stage
Yes
$addFields / $project to store the result
Pseudocode
Pseudocode
for each document:
r = evaluate(radianExpression)
if r is null or missing:
result = null
else if r is NaN:
result = NaN
else if r is ±Infinity:
result = ±Infinity
else:
result = r * (180 / π)
emit { ..., field: result }
We use one angle document. First we store a radian value, then we convert it to degrees, then we nest $acos and convert in one step. Run these in mongosh after inserting the sample data once.
Example 1 — Sample Data
Imagine one angle of π/2 radians (a right angle) and a cosine sample value of 0.8 for later. We save both in a collection named angles.
Conversion is a simple multiply—cheap compared with large sorts or joins. Filter early with $match when only some documents need degrees. Keep radians for math stages and convert late when humans need degrees.
Remember
Key Takeaways
Role: radians → degrees.
Formula:× 180 / π.
Common pair:$acos / $atan then convert.
Inverse:$degreesToRadians.
One line:$radiansToDegrees answers “what is this radian angle in degrees?”
Frequently Asked Questions
$radiansToDegrees converts an angle from radians to degrees. Use it when trig operators return radians but you want human-readable degree values for display or reports.
The syntax is { $radiansToDegrees: <expression> }. The expression can be a field path like "$angle_rad", a literal number, or another numeric expression such as { $acos: 0.8 }.
degrees = radians × (180 / π). For example, π radians becomes 180°, and π/2 radians becomes 90°.
$degreesToRadians converts degrees to radians. The two operators are inverses.
If the argument is null or refers to a missing field, $radiansToDegrees returns null. NaN stays NaN; ±Infinity stay ±Infinity.
Trig operators like $acos and $atan return radians. Wrap them with $radiansToDegrees when you want degrees.
