Roof framing is not a forgiving trade. A half-inch mistake on one rafter can throw off a ridge, create a wavy fascia line, and send the whole stack of rafters back to the saw. The rafter square—especially the ubiquitous speed square—was designed to turn this high-stakes geometry into a simple, repeatable layout process. The rafter book PDF, more often known as the Swanson Blue Book, is the missing link between owning a square and using it like a professional roof framer.
Experienced carpenters rarely calculate roof pitch from memory. They use the printed tables on the body of the square, then cross-reference those numbers with the illustrated instructions in the rafter book. This guide is an exhaustive look at why the rafter book PDF matters, how it works with a speed square, and which speed square models are worth your money in 2025.
For Those in a Hurry: The Short Answer
The most practical choice for most roofers is the SWANSON Tool Co SW1201K Value Pack, because it bundles a 7-inch and a 12-inch speed square with the official Blue Book rafter guide. If you want the best single square with upgraded readability, the Swanson Speed Square Pro 7″ is the professional-grade pick. On a tighter budget, the classic Swanson S0101 7 Inch Speed Square remains the most proven option on Amazon.
Two lower-cost alternatives, the 7 Inch Aluminum Rafter Square and the Aluminum Alloy Rafter Square 7 Inch, are functional layout tools, but they do not include the printed rafter book that makes the Swanson system so effective. If you need the rafter book PDF for reference, pair any of these squares with a phone-based PDF reader or a printed copy of the Blue Book tables.
| Product | Key Feature | Price | Rating | Buy Now |
|---|---|---|---|---|
| Made in the USA, black embossed scales, pro-specific user guide | $14.98 | 4.8 (1,300+) | Buy at Amazon | |
 SWANSON SW1201K Value Pack |
7″ and 12″ aluminum squares with Blue Book | $16.50 | 4.8 (10,200+) | Buy at Amazon |
 Swanson S0101 7 Inch Speed Square |
Classic aluminum rafter square, embossed scales, Blue Book | $9.98 | 4.8 (17,200+) | Buy at Amazon |
 7 Inch Aluminum Rafter Square |
Double-sided engraved scales, budget-friendly | $5.99 | 4.6 (245+) | Buy at Amazon |
 Aluminum Alloy Rafter Square 7 Inch |
Laser-etched scale, multi-angle protractor, red finish | $7.99 | 5.0 (1) | Buy at Amazon |
What Is the Rafter Book PDF and Why Do Framers Search for It?
The rafter book PDF is the digital version of the compact illustrated manual that ships with many Swanson speed square models. Its official common name is the Blue Book, and it is the reference manual that explains every table, notch, and scale stamped onto the square. Search volume for the phrase reveals a simple truth: lots of carpenters buy a speed square at a yard sale or from a hardware store, only to realize the tool is far more powerful than a basic 90-degree triangle.
The Blue Book covers the mechanics of roof framing in plain English. It explains how to lay out common rafters, hip rafters, valley rafters, jack rafters, and even stair stringers. It also walks through the rafter tables printed on the body of the square, so you never have to guess what a number in the 6/12 column actually means. For those who prefer working from a phone or tablet, a scanned rafter book PDF becomes the ultimate field reference.
You do not need a complicated software program to make use of the rafter book. The key is understanding the relationship between roof pitch, horizontal run, and the actual sloping length of the rafter. Once that relationship is clear, the speed square becomes a dedicated roof-framing calculator.
Understanding the Core Mechanics: How a Speed Square Works
A speed square is not just a square. It is a protractor, a miter gauge, a scribing tool, and a rafter table all combined into one aluminum triangle. On a standard Swanson square, the body is a right triangle with a raised flange along one edge. The pivot point sits at the corner where the flange meets the hypotenuse, and the degree scale curves around that pivot.
When a roofer sets the square on a board and rotates it to a particular pitch mark, the tool transfers that roof angle directly onto the lumber. A 6/12 roof pitch, for example, corresponds to the square’s 6-degree mark on the common rafter scale. That mark gives the exact plumb cut angle at the ridge and the matching seat cut angle at the wall.
The rafter tables take the process one step further. Instead of relying on the Pythagorean theorem every time, a framer reads a pre-calculated length factor from the square or from the rafter book PDF. For a 6/12 pitch, the rafter length per foot of horizontal run is 13.416 inches. Multiply that factor by the roof run in feet, and you have the full common rafter length.
Common Rafter Length per Foot of Run
| Roof Pitch | Rafter Length per Foot of Run |
|---|---|
| 3/12 | 12.37 inches |
| 4/12 | 12.65 inches |
| 6/12 | 13.42 inches |
| 8/12 | 14.42 inches |
| 12/12 | 16.97 inches |
These numbers are the backbone of roof framing. The rafter book PDF organizes them in an easy-to-read table, and the square prints them directly on the face of the tool. This redundancy is what separates a professional layout system from a basic carpenter square.
Key Differences at a Glance: Swanson Rafter Square Models
Swanson dominates the speed square category for a reason. The Blue Book is included with most of the company’s standard squares, and the tool is made from heavy-gauge aluminum with black embossed scales. The three most relevant Swanson options are the classic S0101, the upgraded Pro, and the SW1201K Value Pack.
| Product | Best For | Included Book | Price | Buy Now |
|---|---|---|---|---|
| Swanson S0101 |
Everyday common rafter layout | Blue Book | $9.98 | Buy at Amazon |
 Swanson Speed Square Pro 7″ |
Low-glare scales, professional layout | Pro-specific user guide | $14.98 | Buy at Amazon |
| SWANSON SW1201K |
7″ plus 12″ for wide material and hip layout | Blue Book | $16.50 | Buy at Amazon |
Swanson S0101: The Proven Classic
The Swanson S0101 7 Inch Speed Square is the benchmark in this category. With over 17,000 ratings and a 4.8-star average, it is the square that generations of carpenters have carried in their pouches. The blue enamel body and black embossed scales may look simple, but they remain highly readable in direct sunlight. For $9.98, it includes the Blue Book, which means buyers get the full rafter book system rather than just a piece of aluminum.
Swanson Speed Square Pro: Better Visibility in Bright Conditions
The Swanson Speed Square Pro 7″ takes the same geometry and adds black embossed scales on a natural aluminum body. The contrast is slightly different from the classic blue square, and the Pro ships with a pro-specific user guide that focuses on advanced layout tasks. Roofers who work outdoors all day will appreciate the lack of reflective glare on the engraved markings. It is not a revolutionary departure, but it is a refined upgrade that costs only a few dollars more.
SWANSON SW1201K Value Pack: The Ultimate Two-Size System
The SWANSON SW1201K Value Pack is the strongest recommendation for most readers because it solves a real versatility problem. The 7-inch square is perfect for stud layout and standard rafters, but wider engineered lumber benefits from the longer flange of the Big 12 square. The package includes the Blue Book, so the rafter book reference is right in the box. At $16.50 for two squares, this is arguably the best value in the entire speed square market.
How to Use the Rafter Book PDF With a Speed Square: Step-by-Step
Roof framing with a speed square can be broken down into a handful of repeatable steps. The rafter book PDF walks through each one, but the following workflow captures the essential process.
Step 1: Determine the Roof Pitch and Run
The first number you need is the roof pitch, expressed as rise over run. A 6/12 pitch means the roof rises 6 inches vertically for every 12 inches of horizontal run. The run is the horizontal distance from the outside face of the wall to the centerline of the ridge. This dimension is usually half the building width.
Step 2: Look Up the Rafter Length in the Rafter Book PDF
Open the common rafter table and find the pitch column. For a 6/12 roof, the table gives 13.416 inches of rafter length per foot of run. Multiply that factor by the number of feet in the run. If the run is 10 feet, the theoretical rafter length is roughly 134.16 inches.
Step 3: Subtract Half the Ridge Board Thickness
Because the common rafter seats against the side of the ridge board, not its centerline, each rafter must be shortened by half of the ridge board’s thickness. A standard 1.5-inch ridge board requires a 0.75-inch adjustment at the plumb cut. The rafter book PDF makes this correction clear, and experienced framers perform it automatically.
Step 4: Mark the Plumb Cut at the Ridge
Set the pivot of the 7-inch speed square on the top edge of the rafter. Rotate the square until the 6/12 common pitch mark aligns with the edge of the board. Scribe along the hypotenuse to produce the plumb cut. This same angle, when used at the other end of the rafter, forms the tail cut or overhang.
Step 5: Lay Out the Bird’s Mouth
The bird’s mouth is the notch that allows the rafter to sit flat on the top plate. Place the square at the wall line and mark a horizontal seat cut and a vertical heel cut. The seat cut should extend far enough to bear fully on the top plate, but the notch depth should not exceed one-third of the rafter width. The rafter book PDF includes diagrams showing exactly how to set this up without weakening the rafter.
Step 6: Cut and Test One Rafter
Make the cuts on a single rafter first, then use it as a pattern for the rest of the roof. Experienced roofers know that a test rafter is cheaper than a roof full of repetitive mistakes. The speed square makes this process fast enough that cutting a test piece is always the smart move.
Reading the Rafter Tables: Common, Hip, Valley, and Jack Rafters
The rafter tables on the face of a speed square are organized into sections. The first section lists common rafter lengths per foot of run. The second section covers hip, valley, and jack rafters. The third section provides side-cut angles for jacks and hips.
A common rafter runs perpendicular from the wall to the ridge. A hip rafter runs diagonally from the outside corner of the building to the ridge. A valley rafter runs diagonally in the internal corner where two roof planes intersect. A jack rafter is a shortened common rafter that lands on a hip or valley rather than on the ridge.
The rafter book PDF is essential for these advanced members because the geometry is not intuitive. For a hip rafter, the horizontal run is measured along the 45-degree diagonal from the outside corner to the ridge. That run is longer than the common rafter run by a factor of about 1.414. The hip rafter therefore has a steeper-looking cut, a longer overall length, and a side-cut angle where it meets the ridge.
The square’s built-in rafter table already accounts for these relationships. A roofer only needs to read the appropriate column and apply the correction. Without the rafter book, many carpenters struggle to interpret which number applies to which rafter type. That is why the PDF version of the book is such a valuable field reference.
How the Hip and Valley Tables Work
In the speed square rafter table, the hip and valley length factor is always larger than the common rafter factor for the same roof pitch. Suppose the common rafter factor for a 4/12 roof is 12.65 inches per foot of run. The hip rafter factor will be around 17.44 inches per foot of common run. You still apply the number by multiplying it by the common rafter run, not by the diagonal run, which is why the book’s explanation is so important.
Side Cuts and Jack Rafter Shortening
Jack rafters must be shortened according to their spacing along the hip or valley. A rafter book PDF table will show the difference in length per inch of spacing for each pitch. If the jack rafters are spaced 16 inches on center, multiply that spacing by the length difference factor. The result is the amount each successive jack rafter shortens. This information is printed on many speed squares, but the book form is easier to use when laying out an entire roof.
Choosing Between the Rafter Book PDF and the Built-In Tables
Some roofers question whether they need the rafter book PDF at all, since the square already has the numbers printed on it. The answer is that the built-in tables are a memory aid, not a teacher. The numbers on the flange tell you the length factor, but they do not explain when to subtract half the ridge thickness, how to orient the square for a plumb cut, or how to lay out a bird’s mouth.
The rafter book PDF provides the context. It shows visual examples, explains the order of operations, and clarifies the common mistakes that ruin a rafter. A square with tables is a powerful tool; a square plus the rafter book is a complete roofing education in your back pocket.
What the Blue Book Covers
- Common rafter layout for standard pitches
- Hip and valley rafter layout
- Jack rafter shortening and side cuts
- Bird’s mouth depth and heel cut placement
- Stair stringer layout using the same pivot-and-cut method
- Angle conversion for circular saw bevels
- Scribing parallel lines with the built-in notch
This list makes it clear why the phrase “rafter book pdf” is so popular. The book is not an afterthought. It is the instruction manual that unlocks the speed square’s full range of functions. For a homeowner taking on a shed roof or a skilled carpenter framing a complex roof, the same reference guide provides useful, authoritative direction.
Expert Insights: Framing Pitfalls and How to Avoid Them
Professional roofers develop a routine that reduces errors. The rafter book PDF reinforces that routine, but experience still matters. The following pitfalls are the most common issues in speed square roof framing.
Not Accounting for Ridge Thickness
The most frequent mistake in roof framing is using the full building run without subtracting half the ridge board. This error creates rafters that are too long by almost an inch, forcing the framer to trim every piece. The rafter book’s common rafter instructions explicitly state the adjustment, and a digital version on your phone ensures the reminder is always available.
Cutting the Bird’s Mouth Too Deep
A bird’s mouth cut that is too deep dramatically reduces the structural strength of the rafter. The safest approach is to keep the notch depth to no more than one-third of the rafter depth. When laying out the seat cut, use a speed square to check the depth visually. The Blue Book photographs make this clear enough to prevent a costly structural mistake.
Mixing up the Common and Hip-Valley Scales
A 6/12 hip rafter does not use the same plumb cut angle as a 6/12 common rafter. Because the hip rafter runs diagonally, its geometry is different. The speed square includes a separate hip-valley scale for this reason. The rafter book PDF explains how to flip from the common scale to the hip-valley scale without guessing.
Working Without a Test Rafter
Even experienced roofers mock up one rafter before cutting a full set. The speed square makes the first rafter quick to cut, so there is no excuse to skip this validation step. A test rafter catches math errors, pitch errors, and measurement errors before they multiply across the entire roof.
Best Rafter Square Options for Different Budgets
The speed square market has expanded beyond the classic Swanson models, and the low-cost options can be tempting. The best choice depends on how frequently the square will be used and whether the rafter book reference is already in your library.
Swanson S0101: Best for Most Homeowners and DIYers
Buying the Swanson S0101 7 Inch Speed Square is the lowest-risk investment in this category. It has nearly unrivaled buyer confidence, a reasonable price, and the full Blue Book in the package. For someone framing a shed, a small addition, or a set of rafters for a detached garage, this square does everything required.
Swanson Speed Square Pro: Best for Working in Bright Sun
Roofers who spend full days under open sky know that glaring sunlight can wash out stamped markings. The Swanson Speed Square Pro 7″ combats this with black embossed scales that maintain contrast without the blue paint. The pro-specific guide adds depth for advanced layout techniques. For a small premium over the classic model, this is the professional-oriented option.
SWANSON SW1201K Value Pack: Best for Serious Framers
The SWANSON SW1201K Value Pack remains the ultimate buy in this comparison. It includes the compact 7-inch square for everyday layout and the 12-inch square for wide joists, beams, and long rafter stock. The Blue Book is included, and the per-tool cost drops to under $8.25 per square. For any serious roof framing project, this is the smartest package.
Budget Alternatives: Usable but Not Complete
The 7 Inch Aluminum Rafter Square and the Aluminum Alloy Rafter Square 7 Inch are fine basic tools for light-duty tasks. They offer readable scales and a pocket-friendly price, but they do not include a printed rafter book. That means the buyer has to source the rafter book PDF separately and still may not get the same integrated layout system. For occasional use around a workshop, these squares are acceptable. For full roof framing, the Swanson system is worth the additional money.
Final Verdict: The Rafter Book PDF and Speed Square Are a Team
The rafter book PDF is not a replacement for a good speed square, and a speed square without the rafter book only shows a fraction of its potential. The two pieces work together as a complete roof framing system: the square transfers angles to the lumber with mechanical precision, and the book explains which numbers to use, when to use them, and why the geometry works.
For most people, the SWANSON SW1201K Value Pack is the ideal way to start. It includes the classic 7-inch speed square, the larger 12-inch version for wider stock, and the official Blue Book. For a single-square setup, the Swanson S0101 7 Inch Speed Square delivers proven performance at a very low price. Roofers who want better readability and a pro-specific guide will find the Swanson Speed Square Pro 7″ worth the upgrade.
Keep a rafter book PDF on your phone and a speed square in your pouch. Together, they turn roof framing into a predictable, accurate, and satisfying process—one that leaves the guesswork on the ground where it belongs.