Guide · Nov 1, 2026
What Do Sheet Numbers Like A-101 Mean on Construction Drawings?
By Eli Gewirtzman, Owner · Last checked Nov 1, 2026
Under the U.S. National CAD Standard, a sheet number like A-101 has three parts. The letter is the discipline (A for architectural), the first digit is the sheet type (1 for plans), and the last two digits are the sequence (01, the first sheet of that kind). So A-101 is usually the first architectural floor plan, and A-201 the first elevations sheet.
The format comes from the Uniform Drawing System (UDS), Module 1 of the U.S. National CAD Standard (NCS). Not every firm follows it exactly, but most commercial sets and many residential ones come close, so once you know the pattern you can find your way around almost any set.
Part 1: the discipline designator
The first character says which trade the sheet belongs to. UDS Level 1 uses one letter followed by a hyphen. The hyphen is a required placeholder; the standard prefers it to a period because of the dot in file names.
| Letter | Discipline | Letter | Discipline |
|---|---|---|---|
| G | General | Q | Equipment |
| H | Hazardous Materials | F | Fire Protection |
| V | Survey/Mapping | P | Plumbing |
| B | Geotechnical | D | Process |
| C | Civil | M | Mechanical |
| L | Landscape | E | Electrical |
| S | Structural | W | Distributed Energy |
| A | Architectural | T | Telecommunications |
| I | Interiors | R | Resource |
| X | Other Disciplines | ||
| Z | Contractor/Shop Drawings | ||
| O | Operations |
On complex projects, UDS Level 2 adds a second letter and drops the hyphen. The standard’s example: an electrical engineer who designs a phone system might put it on ET (Electrical Telecommunications) sheets, so ET101 rather than E-101.
Part 2: the sheet type designator
The first digit after the letter says what kind of drawing is on the sheet:
| Digit | Sheet type |
|---|---|
| 0 | General (symbols legend, notes) |
| 1 | Plans (horizontal views) |
| 2 | Elevations and profiles (vertical views) |
| 3 | Sections, including wall sections |
| 4 | Large-scale views (enlarged plans, sections or elevations) |
| 5 | Details |
| 6 | Schedules and diagrams |
| 7 | User defined (including typical details) |
| 8 | User defined |
| 9 | 3D representations (isometrics, perspectives, photographs) |
The same digits work for every discipline. S-501 is a structural details sheet, M-601 a mechanical schedule, C-101 a civil plan. A project doesn’t have to use every type.
Part 3: the sheet sequence number
The last two digits count sheets of the same discipline and type. Per the standard:
- Numbering starts at 01. Sheet 00 isn’t permitted.
- Numbers don’t have to be consecutive, so designers can leave gaps for sheets added later.
- Two digits are used even on small projects, so files sort correctly.
So A-101, A-102 and A-103 might be the first floor, second floor and roof plans. The standard also allows matching the number to the floor across disciplines, so A-102, M-102 and E-102 are each discipline’s second-floor plan, though it warns this gets awkward with basements and split levels.
Suffixes for revisions and phases
Small changes are normally shown with revision clouds and an entry in the revision block. When a whole sheet is reissued, UDS lets offices add user-defined characters after another hyphen. Its examples: A-102-R1 for a partially revised floor plan, A-102-X1 for a totally revised one, and A-102-A1 for phase 1 of a sequenced construction plan.
What you’ll see in practice
Real sets vary. You’ll find A101 with no hyphen, A1.01 with a decimal, or a city’s sample index that starts structural at S-100. Sandy Springs, Georgia’s Master Sheet Index Guide, for example, lists C-101 Site Plan, A-101 First Floor Plan, A-201 Elevations and S-100 Foundation Plan, and encourages applicants to follow the NCS naming because many AIA and construction contracts require it. When a set doesn’t match the standard, the sheet index on the cover sheet is the authority.
Where the number shows up
The sheet number sits in the sheet identification block of the title block, usually in the lower-right corner. It also appears inside callout bubbles: a section mark reading 3 over A-301 means “detail or section 3, drawn on sheet A-301.” That’s why consistent numbering matters. If a sheet is renumbered, every callout pointing to it has to change too.
Using sheet numbers when you print
- Order the PDF by sheet number, following the index, before you upload.
- Name files by sheet number (A-101.pdf) so they sort themselves.
- Reprint by sheet number. When only A-102 and A-103 change, you don’t have to reprint the whole set.
At PrintMyPlans.com, every sheet size is $1.95 in black & white and $3.75 in color. Order by 3 PM ET, ships same day.