First Angle vs Third Angle Projection: View Layout and Symbol Explained

What is the difference between first angle and third angle projection?

The difference is only where the views sit on the sheet. In third angle projection the top view is drawn above the front view and the right side view to its right. In first angle projection the top view is drawn below the front view and the right side view to its left. The views themselves are identical.

• Third angle. Each view sits on the side of the front view that it looks at. Looking down from above gives the top view, so it goes above.
• First angle. Each view sits on the far side, as if the part had been rolled over onto the paper. The top view lands below the front view.
• Same part, same views. A hole seen from the right looks the same in both; only its position on the sheet changes.

That is why the two are easy to confuse. A first angle drawing read as third angle still looks like a sensible set of views, and nothing on the sheet looks wrong until the part is made with a feature on the wrong side.

Where does each view go in first and third angle?

Start from the front view, which is the same in both systems. Every other view is placed beside it, lined up with it, on the side that its projection method sets. The table gives the position of each of the usual views relative to the front view.

Most drawings use only three views: front, top and one side. On a third angle drawing that is the usual “L” shape with the top view above and the right side view to the right. On a first angle drawing the same three views form an upside-down “L”, with the top view below and the side view on the left.

Section, detail and auxiliary views are labelled with letters and can sit anywhere, so they do not depend on the projection. Only the plain orthographic views around the front view follow these rules.

Why are they called first angle and third angle?

The names come from geometry. A horizontal and a vertical plane cross to make four quadrants, or angles. Put the part in the first quadrant and it sits between you and the planes; put it in the third and the planes sit between you and the part. Unfolding the planes flat gives the two layouts.

• Third angle, the glass box. Picture the part inside a glass box. Trace each view onto the glass face you look through, then unfold the box. Each view stays next to the face it was traced on.
• First angle, the shadow. Picture a light behind you casting the part’s shadow onto the wall beyond it. Each view lands on the plane behind the part, so after unfolding it ends up on the opposite side.
• No second or fourth angle. In those quadrants the planes fold onto the same side, and the top and front views would be drawn on top of each other.

Many people find third angle easier to learn because the views sit where you would expect them. First angle is just as complete and was the older European convention; both are recognised by ISO 128.

How do you tell which projection a drawing uses?

Look for the projection symbol near the title block: a cone drawn side on, as a trapezoid, beside two concentric circles. In the third angle symbol the trapezoid is on the left with its small end pointing at the circles. In the first angle symbol the circles are on the left, next to the trapezoid’s wide end.

• Why the symbol works. The two circles are the cone seen from its small end. Third angle draws that end view on the small-end side, first angle on the opposite side, so the symbol is itself a two-view drawing in its own projection.
• Words. Many title blocks print “third angle projection” or “first angle projection” beside or instead of the symbol.
• Standard reference. A drawing that cites ASME Y14.5 or Y14.3 is almost always third angle. One that cites ISO standards may be either, so keep looking for the symbol.
• Check a feature. Find a feature that shows on one side only, such as a step, a slot or an angled face, and follow it into the side and top views. Only one projection makes the views agree.

The symbol is a common place for errors on old or redrawn sheets, where it has been copied from another template. If the symbol and the feature check disagree, trust the feature check and ask whoever issued the drawing.

Which countries use first angle and third angle projection?

North America uses third angle; most of Europe, China and India use first angle; Japan and Australia mostly use third angle. Drawings travel with the work, though, so a US shop will see first angle prints from a European customer, and the symbol on each sheet is the only reliable guide.

Companies follow their own drawing standard more than their country’s. A European subsidiary of a US company may draw in third angle, and an old British drawing may be in first angle even if newer sheets from the same firm are not.

What goes wrong when the projection is misread?

The part comes out mirrored, or with features on the wrong face. Reading first angle as third angle moves every side and top view to the opposite side of the part, so a hole, step or chamfer that belongs on the left is made on the right. Symmetric parts hide the error; parts with a handed feature do not.

• Handed brackets and plates. A bracket with its flange on the wrong side will not bolt up to its mating part.
• Holes on the wrong face. A blind hole or counterbore seen in a side view gets drilled from the opposite side.
• Inspection passes. Each dimension can still be correct, so a part checked dimension by dimension may pass and only fail at assembly.
• Old drawings with no symbol. Hand-drawn sheets often lack the symbol, and the company that made them may have used either system.

The guard is the same every time: check the symbol first, then confirm it with one handed feature before cutting. The guide to reading engineering drawings puts this check in its place in the full reading order, and the engineering drawing symbols guide covers the other marks on the sheet.

Does projection matter once the part is in 3D CAD?

No. A 3D model holds the part itself, not views of it, so it has no first or third angle. Projection matters only when the part is read from the 2D drawing. Once it is modelled correctly, any drawing made from the model can be set to either projection in the drawing settings.

That makes a STEP file the safest way to send a part across borders: the shop sees the shape directly, with no views to place. When all you have is the 2D drawing, the projection has to be read correctly once, when the model is made, and every quote and program after that uses the model.

Frequently asked questions

Have this print and need it as a 3D model?

Upload the drawing to Drawing to STEP from PartWork.ai. It reads the projection symbol and the views, models the part from the dimensions and checks it against each view, and you get a STEP and an STL in minutes, from $29.99.

• Any print. A PDF, PNG or JPG, first or third angle, from CAD, a scanner or a phone photo, including old hand-drawn sheets.
• Questions, not guesses. When a dimension is faded, missing or conflicting, we ask you before the model is finished.
• Priced up front. A free check of the drawing sets the price before you pay.

A STEP file is what online machining quotes ask for; see getting a machining quote from a PDF. For the other routes to a model, see CAD drafting services and how to convert a PDF to CAD.

Export-controlled drawings (ITAR/EAR) aren’t accepted.