Framing a roof is one of the most mathematically demanding jobs a carpenter will ever face. Between calculating the pitch, measuring the run, and accounting for the ridge board thickness, a single misplaced decimal can turn a clean roof line into a costly patchwork. The Swanson Rafter Book — often called the Blue Book — is the industry’s answer to that problem, turning complex trigonometry into a series of simple lookup tables and layout steps.
This guide delivers an exhaustive analysis of the Swanson Rafter Book, how it pairs with a speed square, and which versions of the tool-and-book combo deserve a spot in your bag. Whether you’re a DIYer replacing a shed roof or a serious hobbyist building a gable addition, you’ll know exactly which product fits your skill level and budget by the end.
TL;DR: The Swanson Rafter Book and the Speed Squares That Ship With It
For those in a hurry: the Swanson Rafter Book is a pocket-sized reference guide bundled with Swanson speed squares. It eliminates rafter math by providing pre-calculated lengths, angles, and layout numbers for common, hip, valley, and jack rafters. The best overall value is the Swanson SW1201K Value Pack, which includes both the 7-inch and the 12-inch speed squares plus the full Blue Book. For pros who want the latest guide, the Swanson Speed Square Pro 7-inch includes a new pro-specific user guide with expanded rafter tables.
| Product | Price | Rating | Reviews | Key Feature | Buy Link |
|---|---|---|---|---|---|
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$14.98 | 4.8 | 1,300 | Black embossed scales + pro-specific user guide | Buy at Amazon |
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$16.50 | 4.8 | 10,200 | 7-inch + 12-inch squares with Blue Book | Buy at Amazon |
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$9.98 | 4.8 | 17,200 | Classic made-in-USA aluminum alloy, comes with Blue Book | Buy at Amazon |
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$5.99 | 4.6 | 245 | Double-sided engraved scales, budget-friendly | Buy at Amazon |
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$7.99 | 5.0 | 1 | Laser-etched scale, multi-angle protractor in red | Buy at Amazon |
What Is the Swanson Rafter Book?
The Swanson Rafter Book is the instructional manual and reference guide that ships alongside genuine Swanson speed squares. It is a compact, spiral-bound booklet packed with rafter tables, saw miter tables, and step-by-step layout diagrams. Most carpenters refer to it simply as the “Blue Book,” a nod to the blue cover found in the standard 7-inch tool’s packaging.
The guide is not a replacement for a calculator; it is a faster, field-proven alternative. Instead of deriving the rafter length using the Pythagorean theorem or a construction calculator, the user reads the table for the roof pitch, multiplies by the run in feet, and accounts for overhang and ridge thickness. The book removes the need for memorization, which is why it has remained a staple of the framing trade since the original Swanson Speed Square hit the market decades ago.
The content depth varies by product version. Standard 7-inch blue speed squares ship with the classic Blue Book, while the Swanson Speed Square Pro 7-inch includes a newer pro-specific user guide with expanded tables for hip and valley rafters, plus extra layout shortcuts for stair stringers and angle conversions.
Why Rafter Length Math Trips Up Most DIYers
The hardest part of rafter math is not the arithmetic; it’s the number of variables. A common rafter requires knowledge of the run (half the building width minus half the ridge thickness), the roof pitch (rise over run), and the total span. Once those are known, the rafter length must still be adjusted for the ridge board, the birds-mouth cut, and the eaves overhang.
Beginners routinely make three mistakes: using the wrong run dimension, forgetting the ridge board deduction, and confusing plumb cut angles with seat cut angles. The Swanson Rafter Book addresses each of these by providing a consistent sequence: read the pitch, multiply the table value by the run, then follow the layout diagram for the birds-mouth. It turns a multi-step formula into a short, repeatable procedure.
Professional framers use the same tables daily, which speaks to the system’s accuracy. The book’s values are derived from actual geometry, not approximations, so a 6/12 pitch on a 10-foot run yields a rafter length that is correct to within a fraction of an inch. That level of reliability is exactly what a serious hobbyist needs when moving from simple decks to structural roofs.
The Core Mechanics: How the Rafter Book and Speed Square Work Together
A speed square is a triangular tool with a pivoting arm (on some models), a hypotenuse marked with degree graduations, and a body etched with rafter tables. The Swanson Rafter Book provides the instruction sheet for interpreting those etched numbers, making the tool actually usable. Without the book, the tables on the square’s body are a mystery to most beginners.
The mechanics are straightforward. First, determine the roof pitch by placing the square’s pivot point against the rafter edge and rotating it until the desired angle aligns. Second, find the corresponding pitch value in the rafter table printed on the square’s body. Third, open the Blue Book to that pitch section and locate the length multiplier for the run. The result is the rafter length per foot of run.
This combined system is why Swanson speed squares dominate job sites. The tool gives you the angles; the book gives you the lengths. Together, they turn roof framing into a mechanical process rather than a mathematical exercise. The user is effectively working from a cheat sheet that has been refined through decades of field testing.
Key Differences at a Glance: Swanson Rafter Book Versions
Not all Swanson rafter book editions are identical. The classic Blue Book that ships with the standard Swanson S0101 7-inch Speed Square covers common rafters, hip rafters, valley rafters, and basic angle cuts. The newer pro-specific guide included with the Speed Square Pro adds detailed information on jack rafters and includes a more extensive section on stair layout.
| Feature | Swanson S0101 + Blue Book | Swanson Speed Square Pro | Swanson SW1201K Value Pack |
|---|---|---|---|
| Square Size | 7-inch | 7-inch | 7-inch + 12-inch |
| Rafter Book | Classic Blue Book | Pro-specific guide | Blue Book (full) |
| Common Rafter Tables | Yes | Yes | Yes |
| Hip/Valley Rafter Tables | Yes | Expanded | Yes |
| Stair Stringer Layout | Basic | Advanced | Basic |
| Degree Scale | Standard black | Black embossed | Standard black |
| Price | $9.98 | $14.98 | $16.50 |
| Buy Link | Buy at Amazon | Buy at Amazon | Buy at Amazon |
For the homeowner who frames an occasional shed or pergola, the classic Blue Book is entirely sufficient. For the serious hobbyist or finishing carpenter tackling complex roofs, the Pro-specific guide is worth the extra few dollars. The Value Pack remains the ultimate choice because it adds the 12-inch square, which is dramatically more useful for laying out wide rafters and larger structural components.
Using the Rafter Book for Common Rafters: A Step-by-Step Process
The most frequent task in roof framing is cutting a common rafter, and the Swanson Rafter Book reduces it to a four-step sequence once the pitch and run are established.
Step 1: Determine the roof pitch. The pitch is expressed as inches of rise per 12 inches of run, such as 4/12 or 7/12. Measure this from the building plans or physically calculate the rise over the run.
Step 2: Find the line length multiplier. Open the Rafter Book to the page for the corresponding pitch. The table provides a multiplier, such as 12.65 for a 6/12 pitch. Multiply that number by the total run in feet, and the result is the rafter length from the ridge plumb cut to the outside edge of the birdsmouth.
Step 3: Add for overhang and subtract for the ridge board. The book includes guidance on these adjustments, but a practical rule is to add the overhang length and subtract half the ridge board thickness. For example, a 10-foot run at 6/12 pitch gives a base length of 126.5 inches; adding an 18-inch overhang yields roughly 144.5 inches.
Step 4: Mark the plumb cut and birds-mouth. Use the speed square’s pivot point and degree scale at the top of the rafter. Then mark the seat cut at the bottom by aligning the square with the required depth, usually one-third of the rafter width. The Rafter Book provides a diagram showing exactly where each line goes, eliminating the guesswork that causes most DIY failures.
This process works identically whether the user is laying out a single shed rafter or a full gable set. The book’s tables are the same numbers framers have trusted for generations, and presenting them in such a direct format is precisely why the tool remains in production.
Hip and Jack Rafters: Where the Rafter Book Earns Its Keep
Hip and jack rafters are mathematically brutal because they require different length multipliers and compound angles. A hip rafter runs diagonally from the ridge to the corner of the building, and its length depends on both the roof pitch and the angle of the hip in plan view. The average DIYer will not solve that on paper without significant frustration.
Swanson’s rafter tables compress hip and jack rafter calculations into the same lookup format as common rafters. The Blue Book provides separate multipliers for hip and valley rafters, accounting for the diagonal run. Jack rafters, which bear on the hip and run parallel to common rafters, are shortened progressively; the book includes the exact spacing values for standard 16-inch and 24-inch on-center layouts.
The Pro-specific guide that ships with the Swanson Speed Square Pro goes one step further, with additional illustrations for compound miter cuts where jacks meet the hip. For anyone attempting a hip roof on a shop, garage, or addition, this edition is the better investment compared to the classic Blue Book, despite the modest price premium.
The Speed Square Showdown: Swanson vs. Budget Alternatives
Swanson is the original inventor of the speed square, but the market now includes generic rafter squares at significantly lower prices. The question is whether the budget tools perform at the same level when paired with a Rafter Book or standalone layout tasks.
The 7-inch Aluminum Rafter Square and the Aluminum Alloy Rafter Square with laser-etched scale are both viable alternatives for basic marking. They provide the same triangular geometry, degree graduations, and rafter table engravings. However, they do not include the Swanson Blue Book, which means the user must already know how to interpret the tables or rely on external references.
| Feature | Swanson S0101 | 7″ Aluminum Rafter Square | Aluminum Alloy Rafter Square |
|---|---|---|---|
| Includes Rafter Book | Yes (Blue Book) | No | No |
| Build Material | Heavy-gauge aluminum | Aluminum | Aluminum alloy |
| Scale Type | Black embossed | Double-sided engraved | Laser-etched |
| Pivot Point | Yes | Yes | Yes |
| Price | $9.98 | $5.99 | $7.99 |
| Buy Link | Buy at Amazon | Buy at Amazon | Buy at Amazon |
The verdict is nuanced. For pure layout on a flat surface, the generic tools perform nearly identically. The laser-etched scales on the red version are exceptionally legible, and the double-sided engraving on the budget square adds convenience. But the lack of instructional material matters enormously to a beginner; the Swanson’s included Blue Book is effectively a free education in roof framing. For a difference of $4 to $8, the genuine Swanson product is the stronger recommendation for anyone still learning the trade.
Beyond Rafter Lengths: Roof Pitch, Angles, and Scribe Work
The Swanson Rafter Book and the speed square combo extends far beyond rafter calculations. One of the most practical features is the built-in protractor function. By rotating the square’s pivot arm against the edge of a board, the user can lock in any angle from 0 to 90 degrees and transfer it to a workpiece. This is invaluable for cutting purlin angles, birdsmouths, and fascia miters.
The book also covers scribing techniques. The speed square’s body has a scribing notch that allows a pencil or knife to trace a consistent line parallel to the edge. Combined with the rafter book’s guidance on layout spacing, this becomes a fast method for marking multiple joists or rafters at identical intervals.
Another unsung capability is the square’s use as a saw guide. Clamping the speed square to a board and running a circular saw’s shoe along the hypotenuse yields a perfectly square cut every time. The Blue Book documents this application, as well as the miter guide technique for cutting 45-degree and 22.5-degree angles without a miter saw. For a serious hobbyist equipped with only basic tools, these tricks bridge the gap between professional results and garage-level equipment.
Choosing the Right Swanson Rafter Book Combo for Your Skill Level
Selecting the right product depends entirely on the user’s experience and project scope. For the homeowner who needs one or two rafters for a small shed, the Swanson S0101 7-inch Speed Square at $9.98 is the clear entry point. It includes the Blue Book, covers all essential layouts, and costs less than a single trip to the lumber yard for a wasted board.
For the hobbyist or serious DIYer planning a hip roof, garage, or large outbuilding, the Swanson Speed Square Pro 7-inch offers the advanced pro-specific guide and embossed high-visibility scales. The extra $5 over the standard model is justified by the expanded hip, valley, and jack rafter tables alone.
The ultimate recommendation for anyone building a full structure is the Swanson SW1201K Value Pack. At $16.50, it delivers both the 7-inch and the 12-inch speed squares. The larger 12-inch square is significantly better at marking wide boards and transferring long lines, while the 7-inch square remains the all-around pocket tool. Both ship with the Blue Book, making this pack the highest utility-per-dollar option on the market.
Common Mistakes to Avoid When Using the Rafter Book
Even with an exhaustive reference guide, users still make errors. The most common mistake is using the wrong run measurement. The run is the horizontal distance from the outside of the wall plate to the center of the ridge, not the total building width. Forgetting to subtract half the ridge board thickness will add roughly 3/4 inch to every rafter, which compounds across the entire roof.
Another frequent error involves the birds-mouth seat cut. The Rafter Book provides a maximum seat depth, usually one-third of the rafter’s nominal width. Cutting the seat too deep weakens the rafter and creates a structural failure risk. The book’s diagrams explicitly warn against this, but users who skip the reading and rely on the square alone often over-cut.
Finally, users confuse the plumb cut angle at the ridge with the level cut angle at the eave. The speed square’s degree scale measures the plumb cut relative to the rafter edge; the level cut is simply its complement (90 degrees minus the plumb angle). The Blue Book includes a conversion table that lists both, helping users avoid the classic flipped-cut mistake that leaves rafters one angle away from fitting. Checking each cut against the book before sawing will save both material and time.
Expert Insights: How Professional Framers Use the Rafter Book
Professional carpenters rarely carry the full Rafter Book on the job site; they typically memorize the most common pitch multipliers. A framing crew dealing with a 6/12 or 8/12 roof knows the line lengths by heart. But asking them why they still buy the book yields a practical answer: it is the tool for anything outside the routine. Every custom pitch, every odd overhang, and every hip roof with unequal spans sends the crew back to the tables.
Experienced estimators also use the book for material takeoffs. By knowing the exact rafter length multiplier, they can quickly calculate board footage and predict waste. That level of precision is what separates professional bids from amateur guesses, and it is available to any homeowner who takes ten minutes to read the Blue Book’s introduction.
The durability of the book is worth noting. The spiral-bound pages are printed on heavy card stock with moisture-resistant coating, meaning it survives the wet weather of a construction site. For those who prefer digital reference, the same tables are available in PDF form from Swanson’s website, but the physical book has one advantage: it is always in the toolbox when the phone battery dies or the signal drops.
Final Verdict: The Shortcut Is Real
Rafter length math does not need to be a roadblock. The Swanson Rafter Book converts trigonometry into lookup tables, and the speed square turns those tables into precise physical cuts. The combination is a proven system that has seen generations of carpenters through everything from simple gable roofs to complex hip and valley assemblies.
The best buy depends on the project. For most DIYers, the Swanson S0101 7-inch Speed Square is the lowest-risk investment; it is affordable, accurate, and comes with the book. For larger projects and advanced rafters, the Swanson Speed Square Pro provides the expanded pro-specific guide. And for those who want the complete package with both square sizes, the SW1201K Value Pack is the ultimate go-to recommendation.
Mastering rafter math is not about being a genius with numbers; it is about having the right reference guide and knowing how to use it. With the Swanson Rafter Book in the tool bag, the shortcut is always just a page flip away.