A 128° angle is obtuse because it is greater than 90° and less than 180°. Its supplement is 52°, so a 128° angle and a 52° angle side by side make a straight line.
128° is 16/45 of a full circle, or 32π/45 radians. If you face north and turn 128° clockwise, you end up facing between ESE and SE (closest to southeast (SE)).
128° angle facts
| Angle type | Obtuse angle (between 90° and 180°) |
|---|---|
| Supplement (adds to 180°) | 52° |
| Explement (adds to 360°) | 232° |
| Radians | 32π/45 ≈ 2.234021 |
| Gradians | 142.2222 grad |
| Fraction of a turn | 16/45 (35.56%) |
| Degrees, minutes, seconds | 128° 0′ 0″ |
| Compass bearing | between ESE and SE (closest to southeast (SE)) |
Trigonometric values of 128°
| Function | Value |
|---|---|
| sin 128° | 0.788011 |
| cos 128° | −0.615661 |
| tan 128° | −1.279942 |
128° on a protractor
How to draw a 128° angle with a protractor
- Draw a straight line with a ruler. This is the first arm; mark the vertex at one end.
- Place the center mark of the protractor exactly on the vertex and line up the 0° baseline with your line.
- Find 128° on the row of numbers that reads 0° on your line (protractors have two rows running in opposite directions) and make a small dot at the edge.
- Remove the protractor and draw a line from the vertex through the dot. Mark the angle with an arc and label it 128°.
Drawing it a 128° angle without a protractor (rise and run method)
- 128° = 180° − 52°. Draw a straight line, pick a vertex on it, and build a 52° angle on one side as follows; the angle on the other side of the new line is 128°.
- Draw a straight baseline and measure 7.81 inches (about 7 13/16″) along it from the vertex.
- At that mark, draw a line straight up at 90° and measure exactly 10 inches up it.
- Join the top mark to the vertex. The angle at the vertex is 52°, because tan 52° ≈ 1.2799.
Where you see 128° angles
- The Earth turns 128° on its axis in about 8 h 32 min.
- Obtuse angles like 128° appear in reclining chair backs, open laptop screens, fan blades, and the corners of many-sided polygons.
Related angles
128° angle FAQ
What type of angle is 128°?
A 128° angle is an obtuse angle, because it is between 90° and 180°.
What is the supplement of 128°?
The supplement of 128° is 52°, because 128° + 52° = 180°. A 128° angle has no complement, because it is already larger than 90°.
How many radians is 128 degrees?
128° = 32π/45 radians ≈ 2.234 rad. To convert degrees to radians, multiply by π/180: 128 × π/180 = 32π/45.
How do I measure a 128° angle on my screen?
Open the online protractor with 128° preset, or type 128 into its "Type an angle" box. You can then drag the arms onto your own lines to compare.
