Every carpenter who has ever picked up a speed square has faced the same moment of hesitation: the small booklet tucked into the packaging, dense with tables and cryptic numbers, seems more like a puzzle than a manual. Most users skim past it, assuming the rafter book is just filler material, and in doing so they miss the single most valuable reference tool in their apron. That compact booklet, combined with the engraved rafter tables on the square itself, holds the key to laying out common, hip, and valley rafters with speed and precision.
This guide is the ultimate resource for carpenters who want to stop guessing and start reading the rafter book like a pro. It covers the anatomy of rafter tables, step-by-step interpretation of the Swanson Blue Book, practical framing examples, and a detailed buying breakdown of the best speed squares on the market today. By the end, you’ll know exactly how to convert a roof pitch into a cut line, and which rafter square deserves a permanent place in your tool belt.
TL;DR: The Short Answer for Busy Carpenters
For those in a hurry: a rafter book is the instruction manual that ships with most speed squares, most famously the Swanson Blue Book, and it decodes the rafter tables, degree scales, and layout markings printed on the tool’s face. Reading it correctly means understanding three core concepts—roof pitch (rise over run), the constant numbers on the rafter scale, and how to subtract half the ridge thickness from your calculated length. If you want the best all-around experience, the Swanson Speed Square Pro 7″ pairs a professional-grade square with a pro-specific user guide that covers advanced layout techniques. For a budget-friendly classic that ships with the full Blue Book, the SWANSON S0101 7 Inch Speed Square Blue is the industry-standard choice at under $10.
| Feature | Swanson Speed Square Pro 7″ | Swanson SW1201K Value Pack | Swanson S0101 Blue 7″ | 7″ Aluminum Rafter Square | Aluminum Alloy Rafter Square (Red) |
|---|---|---|---|---|---|
| Price | $14.98 | $16.50 | $9.98 | $5.99 | $7.99 |
| Rating | 4.8 (1,300+ reviews) | 4.8 (10,200+ reviews) | 4.8 (17,200+ reviews) | 4.6 (245+ reviews) | 5.0 (1 review) |
| Size | 7-inch | 7-inch + 12-inch Big 12 | 7-inch | 7-inch | 7-inch |
| Guide Included | Pro-specific user guide | Blue Book | Blue Book | Basic instructions | Basic instructions |
| Scale Style | Black embossed | Black embossed | Black embossed | Double-sided engraved | Laser-etched |
| Best For | Pros who want advanced layout instructions | Framers needing a full-size 12″ layout square | Budget-minded pros and DIYers | Bare-bones budget buyers | Shoppers wanting laser-etched visibility |
| Buy Now |  • Buy at Amazon |
 • Buy at Amazon |
 • Buy at Amazon |
 • Buy at Amazon |
 • Buy at Amazon |
What Is a Rafter Book? Understanding the Rafter Tables
A rafter book is the concise reference manual that accompanies rafter squares, serving as a translator for the numeric tables stamped into the tool’s aluminum body. In the case of Swanson’s iconic speed square, the included “Blue Book” has been the default companion since the tool’s introduction, explaining everything from simple 90-degree crosscut marking to complex hip-and-valley rafter layout. The pillar of this discussion, “rafter book pdf,” refers to the digital copies of these booklets that carpenters often seek out after losing the paper version or upgrading to a bare tool without documentation.
The rafter tables themselves are the heart of the rafter book. These tables, printed directly on the square’s face, consist of rows of numbers associated with the rise of the roof, expressed in inches per foot of run. For example, a 6/12 pitch roof rises 6 inches for every 12 inches of horizontal run, and the rafter table will list the corresponding rafter length factor for that pitch. The rafter book explains how to multiply that factor by the total run of the building to get the actual rafter length before any ridge or seat-cut adjustments.
The Confusion Between the Book and the Square
Many carpenters assume the rafter book merely repeats information that is already on the square. In reality, the square provides the raw data, while the rafter book provides the procedure. The square tells you that a 6/12 pitch has a rafter length factor of 13.42 inches per foot, but the rafter book tells you how to apply that number, when to deduct half the ridge board thickness, and how to lay out the seat cut so the rafter seats properly on the wall plate. Both tools are essential, which is why the search for a “rafter book pdf” is so common among carpenters who have the square but lost the manual.
The Anatomy of a Rafter Square: Reading the Scales
Before the rafter book makes sense, the carpenter must identify the different zones of the speed square. Knowing where to look for each piece of data cuts reading time in half and prevents the common mistake of pulling the wrong factor from the wrong row.
Pivot Point and Protractor Scale
The pivot point is the tool’s most critical reference location: the corner where the lip meets the body, marked by a small notch or hole. From that pivot, a protractor scale runs along the hypotenuse, usually from 0 to 90 degrees. When the speed square is rotated against a board’s edge, the protractor scale directly reads the angle of the cut. This scale is the bridge between the rafter book’s pitch tables and the physical act of marking an angled cut on lumber.
The Rafter Scale: A Table Within a Table
The rafter scale occupies a dedicated band on the face of the square, typically labeled with the words “COMMON RAFTERS,” “HIP OR VALLEY RAFTERS,” and “SIDE CUT.” Beneath these headings runs a row of numbers—6, 7, 8, 9, 10, 11, 12—representing rise in inches per foot of run. The numbers below each rise value are the length factors. For instance, at a 6-inch rise, the common rafter factor reads approximately 13.42 inches per foot of run. The rafter book tells the carpenter to multiply this factor by the run in feet, then deduct half the ridge thickness for a perfect fit.
Scribing Notch and Diamond Cutout
Beyond the scales, the scribing notch allows for parallel line layout along a board’s edge, while the diamond cutout enables the square to function as a simple protractor for stair stringers and other angled layouts. These features are covered in detail in the rafter book, but they are secondary to the core reading skill: understanding the rafter factor multiplication.
How to Read a Rafter Book: Step-by-Step
The rafter book’s instructions follow a consistent workflow that applies to nearly every framing scenario. Mastering this sequence transforms the speed square from a simple angle finder into a complete rafter computation tool.
Step 1: Determine Roof Pitch and Total Run
Roof pitch is expressed as a ratio of rise over run, most commonly written as 6/12, 8/12, or 12/12. The first number is the vertical rise in inches, and the second number is the horizontal run in inches. To use the rafter book, you must know both the pitch and the building’s run—the horizontal distance from the outside wall plate to the centerline of the ridge. Always measure the run in feet before consulting the table.
Step 2: Locate the Correct Rafter Table Column
Flip the square to the rafter scale face and locate the row labeled “COMMON RAFTERS.” In Swanson’s design, the numbers 6 through 12 appear in a row, with the corresponding rafter length factors printed beneath. On the Swanson Speed Square Pro 7″, these numbers are black embossed for high contrast, making the table easy to scan even in dim job-site lighting. Read down the column that matches the rise portion of your pitch.
Step 3: Multiply the Factor by the Run
The number listed under the 6-inch column, for example, is roughly 13.42 inches. This factor represents the length of a common rafter for one foot of horizontal run. For a run of 10 feet, multiply 13.42 by 10 to get 134.2 inches, or 11 feet 2 3/16 inches. The rafter book explains that this is the theoretical length from the centerline of the ridge to the outside edge of the wall plate.
Step 4: Make the Adjustments
The rafter book emphasizes a critical correction: subtract half the thickness of the ridge board from the calculated length. If using a standard 1 1/2-inch-thick ridge, deduct 3/4 inch from your total. Many experienced carpenters also account for the roof sheathing thickness and any fascia requirements, though the book primarily covers structural fit. The result is the true length of the rafter from the ridge cut to the seat cut.
Step 5: Lay Out the Seat Cut
The final step in the rafter book’s common rafter procedure is marking the birdsmouth, or seat cut, where the rafter meets the wall plate. The rafter book instructs the carpenter to measure down the rafter at the calculated length, then use the speed square’s protractor scale to draw the plumb cut at the ridge and the level cut at the seat. The seat cut depth should not exceed one-third of the rafter’s total depth to maintain structural integrity.
Decoding the Swanson Blue Book and the Pro Guide
Swanson’s documentation is the gold standard in the industry, and its approach to the rafter book differs slightly between models. The standard SWANSON S0101 7 Inch Speed Square Blue ships with the classic Blue Book, a straightforward manual that has remained largely unchanged for decades. The Blue Book covers the basics: 90-degree crosscuts, 45-degree miters, common rafter layout, hip and valley rafters, and the use of the scribing notch. It is written in plain language, with plenty of diagrams, making it the perfect starting point for apprentices.
The Swanson Speed Square Pro 7″ takes documentation a step further with a pro-specific user guide that expands into advanced techniques like stair stringer layout, polygon angles, and the full function of the rafter tables for irregular pitches. For carpenters who frequently frame complex roofs, the Pro guide is significantly more useful than the standard Blue Book because it explains not just the factor multiplication, but also the geometry that makes those factors work. The square itself retains a compact 7-inch body, but the embossed black scales are easier to read in low-light conditions.
For those who want both the compact square and the full-size version, the SWANSON SW1201K Value Pack bundles the 7-inch speed square with the 12-inch “Big 12” speed square, and ships with the Blue Book. This value set is particularly advantageous on larger timbers where the 7-inch square’s shorter fence struggles to span the full width of a 2×12 or glulam beam. The 12-inch square’s longer body makes layout marks more accurate and reduces the number of times the square must be shifted along the board.
Rafter Book PDF vs. Physical Booklet
The search for a “rafter book pdf” is a rite of passage for many carpenters who have lost their paper manual. Swanson and other manufacturers have historically provided PDF copies of their Blue Book and user guides through their websites, though availability fluctuates as product lines change. The digital format is undeniably convenient: a rafter book pdf can live on a smartphone, be searched for specific keywords, and amplified or printed as many times as needed for the crew.
However, the physical booklet has a distinct advantage in durability and immediacy. The paper version is oil-resistant, folded into a pocket-size format, and always available without needing a charged phone or a clean pair of gloves to operate a touchscreen. The best approach is to keep the physical rafter book in your tool bag and store a PDF copy in your phone’s photo library as a backup. When you upgrade to a square that ships with a different guide, such as the Pro-specific user guide bundled with the Swanson Speed Square Pro 7″, make a point of keeping that manual accessible rather than discarding it with the packaging.
Practical Example: Framing a Shed Roof with a 6/12 Pitch
To make the rafter book’s instructions concrete, consider a simple shed roof with a 6/12 pitch and a total run of 8 feet. Using the common rafter column for 6-inch rise, the factor is 13.42 inches per foot. Multiplying 13.42 by 8 gives 107.36 inches, or 8 feet 11 3/8 inches. The rafter book then instructs the carpenter to deduct half the ridge thickness—typically 3/4 inch—bringing the rafters to roughly 8 feet 10 5/8 inches long.
Next, the speed square is set against the rafter stock with the pivot at the top edge, and a line is drawn across the board at the plumb cut angle corresponding to a 6/12 pitch. At the opposite end, the seat cut is marked 3 1/2 inches down from the plumb line to match a standard 2×4 wall plate. The result is a fully fitted rafter that drops cleanly onto the plate and meets the ridge with a snug joint. This same procedure scales directly to hip and valley rafters by switching to the appropriate column in the rafter book.
Hip and Valley Rafter Factors
For hip and valley rafters, the rafter book’s table lists factors that account for the diagonal run created by intersecting roofs. A hip rafter runs at a 45-degree angle to the common rafters, which increases its effective horizontal run by a factor of 1.414. The rafter book precomputes these values, so instead of performing the square-root math on site, the carpenter simply reads the factor under the “HIP OR VALLEY” heading at the corresponding rise. The seat cut and plumb cut angles for hip and valley rafters are also steeper, and the square’s protractor scale is used to mark these compound angles.
Common Mistakes When Reading Rafter Tables
Even veteran carpenters misread rafter tables occasionally, and the errors are almost always the same few issues. The first and most frequent mistake is selecting the wrong column, particularly confusing the common rafter factor with the hip or valley factor. The second is forgetting to deduct half the ridge thickness, which leaves every rafter 3/4 inch too long and forces the framer to either force the assembly or trim each piece individually. The third mistake is mixing pitch notations: using a 6/12 roof’s degree equivalent (26.57 degrees) when the rafter table expects the rise in inches per foot. Always confirm that the pitch is expressed as a rise ratio before consulting the table.
Another subtle error involves the run measurement. The rafter book assumes the run is measured from the outside face of the wall plate to the center of the ridge. Some carpenters measure from the inside face of the wall or from the outer edge of the sheathing, which shifts every rafter cut off by the difference. Keeping the measurement convention consistent from calculation to layout is more important than the precision of the final mark.
How to Choose the Right Rafter Square and Rafter Book Combo
Choosing between speed squares comes down to the type of framing you do, the documentation you want, and the budget you have available. The classic SWANSON S0101 7 Inch Speed Square Blue is the best entry point for both apprentices and seasoned carpenters who already know the Blue Book backward. Its $9.98 price point, combined with more than 17,000 five-star reviews, makes it the default recommendation for anyone who wants a dependable square without a steep investment.
The Swanson Speed Square Pro 7″ is the better option for professionals who want the enhanced Pro guide and a higher-visibility embossed scale. At $14.98, the price difference is minor, but the included pro-specific user guide covers advanced topics that the Blue Book skips. The SWANSON SW1201K Value Pack at $16.50 delivers the best sheer utility: two quality squares in one package, ensuring the 12-inch version is always available for wide material layout. This is the ultimate choice for a framing crew or a serious hobbyist who works with timber framing.
For bargain hunters, the 7 Inch Aluminum Rafter Square at $5.99 provides a double-sided engraved scale that covers basic layout needs, though it does not include the comprehensive rafter book documentation of the Swanson units. Similarly, the Aluminum Alloy Rafter Square 7 Inch at $7.99 offers laser-etched scales and a multi-angle protractor for a very low price, but its accompanying instructions are minimal compared to the Blue Book. Buyers of these generic squares should download a rafter book pdf from a reputable source so they do not lose access to the instructional content that makes the rafter tables usable.
Expert Tips for Reading a Rafter Book Like a Pro
Experienced carpenters develop habits that make the rafter book even more useful than the manufacturer intended. Always pencil the ridge deduction and seat cut depth directly on the rafter before making any marks, so you never have to re-derive the adjustment after measuring. Keep the rafter book inside the same pouch as the speed square so both never leave the ladder without the other. When working from a rafter book pdf, screenshot the relevant tables and set them as the lock screen wallpaper on your phone for instant reference without scrolling through an entire document.
Another expert practice is to verify the rafter table’s factor against a known theoretical calculation before trusting a new or unfamiliar speed square. A quick check using the Pythagorean theorem for a 6/12 pitch—the square root of (6² + 12²) divided by 12—should yield 13.42. If a budget square’s engraved factor deviates from this value, reject the tool immediately. The reliability of the SWANSON SW1201K Value Pack is why so many framing crews standardize on the Swanson brand: the rafter tables are accurate across every unit, and the included Blue Book matches the tool’s engraved data exactly.
Frequently Asked Questions
What is the best rafter book for carpenters?
The Swanson Blue Book remains the benchmark for clarity and completeness, and it ships free with every standard Swanson speed square. The Pro-specific user guide included with the Swanson Speed Square Pro 7″ is the more advanced alternative for complex roof layouts.
How do you read a common rafter table on a speed square?
Locate the “COMMON RAFTERS” heading, read the factor beneath your pitch’s rise number, and multiply it by the run in feet. Subtract half the ridge thickness from the result to get the final rafter length.
Can I use a rafter book pdf instead of a physical manual?
Yes, a rafter book pdf is perfectly functional for reference and searchability. However, the physical manual survives job-site conditions better and requires no battery or screen access, so the best practice is to keep both.
Final Verdict: Master the Rafter Book, Master the Frame
Reading a rafter book is not an act of memorization; it is a systematic skill that converts roof pitch geometry into accurate cut lines. Once the rafter table, the run measurement, and the ridge deduction become second nature, every subsequent roof layout becomes faster and more confident. The speed square and its accompanying rafter book form a matched pair, and buying a square that includes the proper documentation—rather than relying on a bare-bones generic tool—is the shortest route to framing mastery.
For the best combination of quality, documentation, and value, the Swanson S0101 7 Inch Speed Square Blue is the top all-around pick, while the Swanson Speed Square Pro 7″ is the definitive upgrade for professionals who want the advanced Pro guide. Your next roof starts with a single cut, and that cut starts with knowing exactly what those tiny numbers on the rafter square mean.