Home › Printables › Printable Protractor
Printable Protractor
Quick answer: A 180° protractor with a 3-inch radius, graduated every degree and numbered both ways. Print at 100% / Actual Size, mount it on card, and pierce the centre cross before use.
An actual-size 180-degree protractor in Letter and A4, with a calibration bar, plus the mitre angles worth memorising and how to read a roof pitch with it.
Download — print at 100% / Actual Size
Download US Letter Download A4
Every sheet carries a calibration bar. Measure it before you use the printout — if it is not exactly 4 inches and 100 mm, your printer scaled the page.
What is on the sheet
A 180° protractor with a 3-inch radius, graduated every degree, numbered every ten in both directions — the outer scale reading left to right and the inner scale right to left, exactly as a moulded protractor does. There is a pierce cross at the origin so you can pin it accurately over a drawing.
- Every 1° — short tick
- Every 5° — medium tick
- Every 10° — long tick, numbered both ways
Print it at the right size — this is the whole game
The usual culprit is a printer driver defaulting to “Fit to page” or “Shrink oversized pages”, which silently reduces the sheet by 2–6% to keep clear of the unprintable margin. In your print dialogue:
- Set Scale to 100%, or choose Actual Size — not “Fit”.
- Turn off Shrink oversized pages if your reader offers it.
- Pick the paper size that matches the file you downloaded — Letter or A4, not the other one.
- Print from a PDF reader rather than a browser preview where you can. Browser print pipelines rescale more often.
If the bar comes out consistently short by a fixed percentage, you can compensate by setting a custom scale — a bar measuring 3.9″ instead of 4″ means you printed at 97.5%, so reprint at 102.5%.
Using it
- Cut around the outer arc and along the baseline.
- Pierce the centre cross with a pin or an awl.
- Place the pierce point exactly on the vertex of the angle, with the baseline along one leg.
- Read where the other leg crosses the arc. Use the scale that starts at zero on the leg you aligned — that is what the two number rows are for.
Angles worth knowing
| Angle | Where it comes up |
|---|---|
| 22.5° | Octagon mitre — eight-sided frames, columns, gazebo posts |
| 30° | Hexagon mitre, isometric drawing, common roof pitch (~7/12) |
| 36° | Pentagon mitre |
| 45° | Square corner mitre, 12/12 roof pitch |
| 60° | Equilateral triangle, hexagon internal angle |
| 67.5° | The other half of an octagon corner |
For a mitre joint, each piece is cut at half the corner angle. A 90° corner takes two 45° cuts; a 135° octagon corner takes two 67.5° cuts.
Measuring a roof pitch with it
Hold a level horizontally against the rafter or the roof surface, place the protractor’s baseline along the level, and read the angle the roof makes. Convert with our roof pitch chart — 26.57° is a 6/12 pitch, 18.43° is 4/12, 45° is 12/12.
Frequently asked questions
How do I print a protractor to actual size?
Set the print scale to 100% or Actual Size rather than Fit to Page, then check the calibration bar on the sheet measures exactly 4 inches. A protractor printed at 97% reads every angle correctly — angles are scale-invariant — but the radius will be wrong if you are using it to step off distances.
How do I use a printable protractor?
Cut around the arc, pierce the centre cross, place that point on the vertex of the angle with the baseline along one leg, and read where the second leg crosses the arc. Use whichever of the two number scales starts at zero on the leg you aligned.
What angle do I cut for an octagon?
22.5 degrees on each piece. An octagon's corners are 135 degrees, and a mitre joint splits the corner angle in half — so each of the two pieces is cut at 67.5 degrees from square, which is 22.5 degrees off the 90-degree setting on most mitre saws.
Can I use a paper protractor accurately?
Yes, if you mount it on card first. Loose paper flexes as you press it against a drawing, which is the main source of error. Spray-mount it to thin card and cut through both layers.