How to set units to inches in AutoCAD

Choose the right inch format — decimal or architectural

Imperial drafting uses two common length formats, and you pick the one your discipline expects.

Decimal inches express lengths as plain decimals — 23.62 — which suits mechanical and engineering work. Architectural format expresses lengths as feet and inches with fractions — 1'-11 5/8" — which is the convention for US building drawings. AutoCAD treats both as 'inches' internally; the difference is purely how the number is displayed.

You set this in the UNITS dialog under 'Length' > Type: choose Decimal for decimal inches, or Architectural for feet-and-inch display. Pick the precision your office standard requires (for architectural, often to the nearest 1/8" or 1/16"). The choice is cosmetic in the sense that it never changes a real size, but getting it right makes your dimensions read the way your reviewers expect.

Set the insertion scale to inches

Display format aside, the setting that governs block scaling is the insertion scale, and for an inch drawing it should be Inches.

Type UNITS, and in the 'Insertion scale' panel set 'Units to scale inserted content' to Inches. Or set it on the command line: INSUNITS, Enter, then 1 (the code for inches). With INSUNITS at 1, AutoCAD knows one drawing unit equals one inch, so when you insert a millimetre block it divides by 25.4 to convert, and a 600 mm cabinet lands as about 23.62 inches — true size in your inch drawing. If your template works in feet rather than inches as the base unit, set INSUNITS to 2 (feet) to match. The point is that the insertion unit must reflect what one drawing unit really means.

Start from the imperial template (acad.dwt)

The clean way to begin an inch drawing is from the imperial template, so the units are right from the start.

When you create a new drawing, choose acad.dwt — the imperial template, configured for inches — rather than acadiso.dwt, which is the metric (millimetre) template. acad.dwt sets decimal inch defaults; if you want architectural feet-and-inch display you switch the length type in UNITS afterwards, or start from an architectural template if your office provides one. Starting imperial means INSUNITS, text heights and dimension defaults are already inch-based. If you always work imperial, set acad.dwt (or your firm's architectural template) as the default in Options > Files > Template Settings so new drawings start in inches automatically.

Typing feet and inches at the command line

Entering imperial measurements has its own grammar that catches metric users out, so it is worth learning the syntax.

When architectural units are on, AutoCAD assumes a plain number is inches: type 18 for 18 inches. For feet, append a foot mark: 3' is three feet. For feet and inches together, type them run-on: 3'6 means three feet six inches (the inch mark is optional). For fractions, separate with a hyphen or a space inside the inch part: 3'6-1/2 is three feet, six and a half inches. Never put a space where AutoCAD might read the entry as finished. Once this syntax is in your fingers, dimensioning and coordinate entry in an architectural drawing feel natural; until then, it is the single most common stumble in imperial AutoCAD.

Inserting the metric blocks into an inch drawing

Here is the practical question for this site: the blocks are millimetres, your drawing is inches — does that work? Yes, cleanly, provided the insertion scale is set.

With INSUNITS at 1 (inches), insert a block as normal. AutoCAD reads the block's millimetre unit, compares it to your inch drawing, applies the 25.4 conversion, and the block lands at true real-world size — a 1700 mm bath comes in at roughly 66.9 inches. You type no scale factor; the conversion is automatic because both sides declared their units. This is the whole reason INSUNITS exists: it lets a metric library serve an imperial drawing (and vice versa) without anyone doing arithmetic. If a block comes in about 25 times too big or too small, that is the tell-tale sign the insertion unit is set to Unitless rather than Inches.

Save an inch template so it persists

As with any unit setup, configuring one drawing does not carry to the next — new files inherit from their template. So build an imperial template and start from it.

Begin from acad.dwt or your architectural template, set the length type (decimal or architectural) and INSUNITS to 1, add your standard layers, text and dimension styles, and a title block, then SAVEAS to an .dwt with a clear name. New drawings started from it are in inches with your standards and the correct insertion scale, so the metric blocks here always convert and land true. Sharing that template across the office keeps every imperial drawing consistent — same display format, same insertion behaviour — which is exactly what keeps block sizes and dimensions reliable across a project.