How to Read Building Plans and Blueprints: A Beginner's Guide
Last updated: November 2026 · From the KRMPLANS team, designers of DIY building plans
Quick answer: To read building plans, start with the floor plan for overall size, then the elevations for heights, the sections for how parts stack together, and the framing drawings and details for each member. Dimensions are in feet and inches (12'-6" means 12 feet 6 inches), spacing like 16" O.C. is measured center to center, and a 2x4 actually measures 1-1/2" x 3-1/2".
A set of plans can look overwhelming the first time you open it, with dozens of lines, symbols and abbreviations on every page. This guide is for first-time DIY builders who want to read a plan set with confidence. You will learn what each drawing type shows, how scale and dimensions work, what the common abbreviations mean, and how to use a cut list to save lumber and time.
Key Takeaways
- A plan set moves from big picture to detail: floor plan, elevations, sections, framing plans, details, then the cut list and shopping list.
- Always build from written dimensions, never by measuring the drawing with a ruler.
- O.C. means "on center," measured from the center of one member to the center of the next.
- Nominal lumber sizes are larger than actual sizes. A 2x6 is 1-1/2" x 5-1/2".
- Read the whole set once before cutting anything, and mark questions as you go.
What Is Included in a Set of Building Plans?
A typical plan set for a shed, coop, pergola or cabin includes a floor plan, exterior elevations, cross sections, framing plans, construction details, and material lists. Each drawing answers a different question about the same building.
- Floor plan: the view from above, cut horizontally about 4 feet up. It shows overall length and width, wall locations, door and window openings, and interior layout.
- Elevations: straight-on views of each side (front, rear, left, right). They show heights, roof pitch, window and door placement, siding and trim.
- Sections: a vertical slice through the building, showing how the foundation, floor, walls and roof connect and how tall each layer is.
- Framing plans: drawings of the floor, wall and roof framing, showing each joist, stud and rafter with spacing and size.
- Details: enlarged drawings of specific connections, like a rafter seat, post base, or window header.
- Cut list: every piece of lumber with its size, length and quantity, often grouped by assembly.
- Shopping list: the materials to buy, including lumber in stock lengths, sheet goods, fasteners and hardware.
KRMPLANS plans, for example, are PDF downloads in US Letter size with imperial measurements, and include a floor plan, elevations, framing drawings, illustrated step-by-step build steps, a shopping list, a master cut list and cut diagrams.
How Do You Read Scale and Dimensions on a Plan?
Scale tells you how the drawing relates to real size, but on a DIY build you should always work from the written dimensions, not by measuring the paper. Printing a PDF can shrink or stretch a drawing slightly, so a scaled measurement can be off.
Scale
Common architectural scales are 1/4" = 1'-0" (one quarter inch on paper equals one foot) for floor plans and elevations, and 1" = 1'-0" or larger for details. Some drawings are marked "NTS," meaning not to scale, so the dimensions are the only reliable numbers.
Dimension conventions
- Feet and inches: 12'-6" is 12 feet 6 inches. 3/4" is three quarters of an inch.
- Dimension strings: a chain of measurements along one side. The overall dimension should equal the sum of the parts; if it does not, ask before cutting.
- Where dimensions are taken: plans usually measure to the outside face of framing, to the center of posts or openings, or to the edge of the foundation. Check the notes or details to see which.
- Rough openings: window and door sizes listed as R.O. are the framed opening, usually about 1/2" to 1" larger than the unit itself. Confirm with the manufacturer's installation instructions.
- Spacing: 16" O.C. means 16 inches from the center of one stud, joist or rafter to the center of the next. 24" O.C. is the other common spacing.
What Do Common Building Plan Abbreviations Mean?
Abbreviations save space on drawings. The table below covers the ones you will see most often on residential and backyard plans.
| Abbreviation | Meaning | What it tells you |
|---|---|---|
| O.C. | On center | Spacing measured center to center, e.g., 16" O.C. |
| PT | Pressure-treated | Lumber treated for ground contact or exterior exposure |
| OSB | Oriented strand board | Sheathing panel for walls, roofs and floors |
| CDX | Construction-grade plywood, exterior glue | Common sheathing plywood |
| LVL | Laminated veneer lumber | Engineered beam or header, stronger than sawn lumber of the same size |
| TYP. | Typical | The same detail applies at every similar location |
| SIM. | Similar | Close to the referenced detail, with minor differences |
| R.O. | Rough opening | Framed size of a door or window opening |
| T&G | Tongue and groove | Interlocking boards or panels |
| DBL / (2) | Double | Two members side by side, e.g., (2) 2x10 header |
| EQ. | Equal | Divide the space into equal parts |
| NTS | Not to scale | Use the written dimensions only |
| A.F.F. | Above finished floor | Height measured up from the finished floor |
Common symbols include a dashed line for something hidden or overhead (like a beam or roof edge above), a circle or flag with a number pointing to a detail on another page, and section cut lines with arrows showing which way you are looking.
What Is the Difference Between Nominal and Actual Lumber Sizes?
Nominal size is the name of the board, and actual size is what it measures after drying and planing. A 2x4 is actually 1-1/2" x 3-1/2". As a rule, dressed dimensional lumber loses 1/2" from nominal sizes of 2" to 6" and 3/4" from sizes over 6" (Missouri University of Science and Technology: Sizes of Structural Lumber).
| Nominal size | Actual size |
|---|---|
| 1x4 | 3/4" x 3-1/2" |
| 1x6 | 3/4" x 5-1/2" |
| 2x4 | 1-1/2" x 3-1/2" |
| 2x6 | 1-1/2" x 5-1/2" |
| 2x8 | 1-1/2" x 7-1/4" |
| 2x10 | 1-1/2" x 9-1/4" |
| 2x12 | 1-1/2" x 11-1/4" |
| 4x4 | 3-1/2" x 3-1/2" |
| 6x6 | 5-1/2" x 5-1/2" |
Lengths are different: an 8-foot board is usually sold at 8 feet or slightly longer. Rough-sawn lumber from a local mill may be close to full nominal size, so measure before you cut.
How Do You Use a Cut List Efficiently?
A cut list tells you every piece to cut, and using it well means grouping cuts by board length so you waste as little lumber as possible.
- Read the whole plan set first. Understand each assembly before you cut, and note anything unclear.
- Match cut list to shopping list. Check that the stock lengths you bought cover every piece, and follow the cut diagrams if your plan includes them.
- Cut longest pieces first. Rafters, joists and plates come from full boards. Use offcuts for blocking and short pieces.
- Group by size and length. Cut all identical pieces at once with a stop block for consistency.
- Label every piece. Write the cut list part name or number on each board in pencil.
- Check off as you go. Mark each line on a printed copy so nothing is missed or duplicated.
- Verify with a test fit. For angled cuts like rafters, cut one pair, test it, then use it as a template.
Our guide on how to download, organize and print your PDF building plans explains how to print at actual size and keep pages organized on site, and our backyard project checklist covers what to prepare before you start.
Common Mistakes to Avoid
- Scaling dimensions off a printed page instead of reading the written numbers.
- Confusing O.C. spacing with the gap between boards.
- Assuming a 2x4 is 2 inches by 4 inches when laying out walls or checking heights.
- Ignoring "TYP." notes, then building only one of several identical details correctly.
- Cutting short pieces from long boards first and running out of full-length stock.
If you want practice reading a complete set, a compact project like our 24x14 shed with porch plans or the 12x16 sage green office studio plans includes every drawing type described above. Our step-by-step shed building guide shows how those drawings translate into a build sequence.
DIY 24x12 Tack Shed Plans: Horse Feed Storage, Sliding Barn Doors PDF: instant PDF download with illustrated steps, a shopping list and cut lists.
Frequently Asked Questions
What does O.C. mean on building plans?
O.C. stands for "on center." It means the spacing is measured from the center of one framing member to the center of the next, such as studs at 16 inches O.C. It is not the gap between boards.
What is the difference between a floor plan and an elevation?
A floor plan is a view from above that shows length, width, walls and openings. An elevation is a straight-on side view that shows heights, roof pitch and the exterior appearance. You need both to understand a building fully.
Why is a 2x4 not actually 2 by 4 inches?
The 2x4 name is a nominal size from the rough-sawn board. After drying and planing smooth, the finished board measures 1-1/2 by 3-1/2 inches. Plans and cut lists account for the actual size.
Should I measure drawings with a ruler?
No. Printing can slightly change a drawing's size, and some drawings are not to scale. Always use the written dimensions, and ask the plan designer if a dimension is missing.
What does TYP. mean on a blueprint?
TYP. means "typical." The note or detail applies to every similar location in the building, not just the one where it is labeled.
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Put Your Plan-Reading Skills to Work
Once you can read a floor plan, elevations and a cut list, any backyard project becomes far less intimidating. Browse our garden shed plans for complete PDF plan sets with framing drawings, cut diagrams and shopping lists in feet and inches.
