Syntax
ATAN(number)
| Parameter | Description |
|---|---|
| number | Parameter of the ATAN function. |
Examples
Arctangent of 1
Formula
=ATAN(1)
Returns ~0.7854 (π/4 radians or 45°). A slope of 1 (rise equals run) corresponds to a 45° angle.
Roof pitch to degrees
Formula
=DEGREES(ATAN(6/12))
Returns ~26.57°. A 6/12 roof pitch (6 inches rise per 12 inches run) is about 26.6 degrees from horizontal.
Slope to angle
Formula
=DEGREES(ATAN(0.15))
Returns ~8.53°. A road grade of 15% (0.15 rise/run) corresponds to about 8.5 degrees.
Common Errors
#VALUE!
Non-numeric input returns #VALUE!. ATAN accepts any number (unlike ASIN/ACOS which are limited to -1 to 1).
Tips
Accepts any number
Unlike ASIN and ACOS, ATAN accepts any real number from -∞ to ∞. The result is always between -π/2 and π/2 (-90° to 90°).
Slope to angle conversion
Grade percentages are rise/run ratios. ATAN converts them to angles: a 10% grade = DEGREES(ATAN(0.10)) ≈ 5.7°.
Use ATAN2 for full range
ATAN only returns angles in the right half of the unit circle (-90° to 90°). Use ATAN2(x,y) to get the full -180° to 180° range based on quadrant.
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