Angle Builder Game
Use the protractor to build a target or missing angle.
Daily and practice math puzzles
Loading math puzzle…
Controls & saved progress
Drag the protractor ray or focus the slider. Arrows change one degree; Home/End reach its limits. The four adjustment buttons also work by keyboard.
Saved progress stays in this browser when available.
Best scores are separate for each level. Hints and Undo mark assistance; assisted rounds do not replace an unaided best.
How to Play Angle Builder
Construct an angle from the right-facing 0° baseline, measuring counterclockwise. Drag the ray on the protractor, move the degree slider or use the −5°, −1°, +1° and +5° buttons. The current angle is shown as a number and a ray, with its angle type below the controls.
Easy asks for a stated target between 0° and 180°. Normal asks for the missing part of a straight angle: subtract the known angle from 180°. Hard asks for the missing part of a full turn, using two known angles and a 360° total. Hard can require a reflex angle greater than 180°.
Choose Check angle after constructing your answer. A construction within 1° of the exact answer is accepted; this tolerance is shown in the game. Feedback gives the required calculation and your angular error. The protractor is a learning diagram and is not a measurement of a physical object or device orientation.
Worked Examples: Straight Angles and Full Turns
Two adjacent angles on a straight line total 180°. If one is 65°, the other is 180° − 65° = 115°. Build 115° from the baseline. This is an obtuse angle, because it is larger than 90° and smaller than 180°.
Angles around a point total 360°. If two are 60° and 40°, the missing angle is 360° − 60° − 40° = 260°. This is a reflex angle. Use Hard’s full-circle scale or its slider to reach angles beyond the upper semicircle.
An acute angle is smaller than 90°, a right angle is 90°, and a straight angle is 180°. A full turn is 360°. The ray returns to the same direction after a full turn, but its measured turn is different from 0°. Read the requested angle and the numeric output together when you work with reflex and full-turn values.
Keyboard, Daily Geometry and Records
With the slider focused, arrow keys adjust one degree at a time. Home moves to 0° and End moves to the current maximum. Tab reaches the fine-adjustment buttons and Check angle. These controls provide an alternative to dragging and work on narrow screens. Undo restores the previous adjustment and marks assistance.
Daily is repeatable for the selected level and UTC date. Practice provides another target through New puzzle. The selected ray position and your checks save separately by mode and level. Daily changes at midnight UTC. Saved data stays in the current browser and does not sync to another device.
A first-check construction can earn 100 points. Extra checks and hints lower that score. Assisted rounds do not replace an unaided best, and only the first completion of a distinct puzzle adds to the solved count. A completed task also appears in the shared math-practice calendar.
Frequently Asked Questions
What is the accepted angle tolerance?
A construction at most one degree from the exact required angle is accepted. The game shows both the target calculation and your current measurement.
How do I build an angle above 180 degrees?
Choose Hard for the full-circle scale, then drag the ray or use the slider and degree buttons to construct a reflex angle.