If you’re planning on doing any carpentry–successfully–you’ll need a way to mark a straight line. After researching at least 20 combination squares and testing six during the final phase of a whole-house remodeling project, we’re convinced that the best option for most people is the Irwin 1794469 12-inch Combination Square (about $11). You can find pro versions of this all-purpose marking tool that cost hundreds of bucks, but the Irwin model is a solid alternative that works well for a fraction of the price. It surpassed the other combination squares we tested thanks to several details that differentiate an excellent tool from an average one; in particular, we liked the smooth machining of the main body, the evenly chamfered edges, the nice powder-coated finish, and the fact that it’s a touch heavier than the rest, which gives it a truly solid feel. Like some other combination squares we tested, the Irwin has a zinc body and a stainless-steel ruler, so it won’t rust or corrode. Our carpenter test crew kept coming back to the Irwin because it got the job done and it feels like a high-quality tool—much higher quality, in fact, than its price would suggest.
If you can’t get the Irwin, we also like the Swanson 12-inch Combo Square (about $9). It has all of the same functions; it’s simply not as polished as our main pick.
I have 10 years of experience in the construction industry, first as a carpenter, then as a foreman, and finally as a jobsite supervisor running multimillion-dollar remodeling projects in the Boston area. During those years, I spent a good deal of time measuring and cutting, and I was never far from a combination square. Over time, I’ve probably owned seven or eight of them, and because of that, I have a pretty good eye for what makes a good one and what makes a not-so-good one. In addition to my work in the trades, I’ve been writing about and reviewing tools since 2007 with articles appearing in Fine Homebuilding, The Journal of Light Construction, Popular Mechanics, Popular Science, This Old House, and Tools of the Trade, where I’m a contributing editor. Recently I also spent three and a half years fully gutting and renovating my 100-year-old farmhouse. (A lot of measuring and cutting there.)
A combination square is a useful tool for layout and marking, particularly with any woodworking project. Every carpenter I’ve ever met carries one. At its most basic, the tool gives you a way to draw a line square off the edge of a board. It can also mark one at a 45-degree angle. The ruler slides within the tool, and you can lock it in place with a knurled thumb turn. This design lets you easily mark a specific measurement off the edge of a board (say, if you’re going to cut a notch) or draw a line parallel to the edge of the board. You can also remove the ruler and use it in situations where a tape measure is impractical. This article at StartWoodworking explains even more uses for the tool, from calibrating a table saw to checking the end of a board for square.
Among combination squares, the models with the 12-inch rulers are the most useful because they can extend a square line a little over 10½ inches, which is enough for most common widths of lumber (for lengths beyond that, you can flip the square to the other side of the board and complete the line). The ones with 16-inch rulers are unwieldy, and the 6-inch models are too small. People consider the 12-inch models to be the standard, and basically every carpenter has one somewhere in the toolbox.
For even a low-cost combo square, however, it’s important to choose one with a stainless-steel blade. Regular steel blades will rust to the point where the markings become impossible to read. Some models, like this Johnson (about $6) and this Stanley (about $11), have a coated blade to prevent corrosion, but once the coating chips off, the blade is toast. Getting a stainless ruler is worth the $5 or $6 upgrade.
For our tests, we came down to six finalists, all but one with a zinc body and a stainless-steel ruler. The oddball was the Swanson TC131 (about $10), with its plastic composite body. We wanted to see how it would stack up against models with durable metal. We chose tools based on the manufacturer’s reputation as well as on the customer feedback at retailers like Amazon, Home Depot, and Lowe’s. I’m familiar with all of the companies represented, and all are known for quality hand tools.
To test our selection of combo squares, we first confirmed whether they provide a perfect 90-degree angle, and we did any necessary calibrations to correct them. We then used each one during a large garage shelving project, paying attention to overall handling (how easily the ruler slides, the action on the knurled knob, and the ease of flipping the ruler in the base). I also checked each metal ruler for accuracy with a Lixer Tape Measure Inspection Tool (all of them were well within 1/64 inch of accurate).
Of the six combination squares that we tested, the best for most people is the Irwin 1794469 12-inch Combination Square (about $11). What impressed us is the high level of fit and finish that the Irwin offers for a relatively low price. The edges are evenly chamfered over, and the body has a powder-coated finish to it. The ruler slides easily, and the knurled drawbolt that locks it in place is simple to access and use. Simply put, the Irwin was the combination square we enjoyed using the most. In fact, it was far more polished and professional-looking than other tools that closed in on the $20 mark. With all of my experience using combination squares, I would have guessed it to be at least twice the price, just from the way it handles.
Beyond the look and feel, the Irwin has a zinc body and a stainless-steel ruler, neither of which will rust or corrode over time. Both of these features were common among the better squares we tested, but not available on all of them. Many inexpensive combo squares have steel blades coated with a protective finish; once the coating chips off (and it will chip off), the blade quickly deteriorates to the point where you can’t read it.
Each of the four edges of the Irwin ruler has a different incremental measurement scale. Three are imperial (⅛, 1/16, and 1/32 inch) and the last is metric (millimeters). You can remove the ruler from the base and flip it so that you can change which scale is on the outer or inner side of the tool, depending on the gradations and precision you’re looking for. Some combo squares, like the Craftsman (about $13), have the imperial scale on all four sides. Personally, I’ve always found the metric scale useful if for nothing other than measuring metric nuts and bolts. When I’m working in the imperial scale, flipping the ruler in order to move the metric scale out of the way is easy enough.
Straight from the packaging, the Irwin was a cat’s whisker out of square (literally, just a pencil line off). Correcting this was a simple process that took maybe 90 seconds. Learning how to check for square and make an adjustment is worthwhile, and it isn’t a big deal at all (this video explains everything). In fact, all but one tool that we tested was out of square upon arrival.
Every combination square comes with a small metal scribe stored in the base of the handle. You can use this item, which looks like a nail, to scratch a precise line in lieu of a pencil. On most combo squares, the scribe has a threaded piece that screws into the base to store it securely. On the Irwin, however, the scribe is only pressure-fit into the handle. The connection stays tight and allows you to remove the scribe quickly, but I’d prefer the more secure connection of a threaded piece. In the end, though, you might never use the scribe. I was about three years into my carpentry career before I even knew it existed, and since then I haven’t used it a single time.
If the Irwin is unavailable, consider the Swanson 12-inch Combo Square (about $9). The least expensive metal-bodied square we looked at, this tool satisfies the basic requirements (zinc body, stainless-steel ruler). It was also the only combo square we tested that was perfectly square out of the package. Its base isn’t as robust as that of the Irwin, and the level of finish is lower. When I run my fingers along the edges of the ruler, I can feel slight inconsistencies; they’re not severe to the point where they disrupt a pencil line, but their presence is a reflection of the tool’s lower price. Ultimately, this slight reduction in quality does not impede the tool’s overall function.
Amazon customer feedback for the Swanson currently sits at a decent 4.1 stars out of five, across 25 reviews. Some negative comments say that the tool arrived out of square—a situation that’s more likely than not. Learning to test and calibrate your combo square is essential to owning one.
The Empire e250 (about $17) and the Craftsman (about $13) are the same tool except that the Empire has blue liquid in the level vial and the Craftsman has the traditional yellow. Both of them are nice tools with only imperial markings. (Empire also offers the $25 e250M with only metric markings as well as the $15 e250IM with both imperial and metric.) Both were just a whisker off out of the box, yet easy to adjust. They’re lighter than the Irwin, however, and they feel less solid and durable. The Swanson Savage SVC133 (about $14), which has a more modern design, arrived significantly out of square. Of the metal squares we tested, it was the lightest model, which none of our testers cared for.
Lastly, we looked at the Swanson TC131 (about $10), which has a composite handle and feels very light. With the Irwin and the others priced only a few dollars more, choosing a tool with a more durable metal base makes more sense.
The other option we considered in addition to a combo square is a 7-inch rafter square, the most well known of which is the Swanson Speed Square (about $10). Popular with carpenters, these triangular tools can mark any angle from 0 to 90 degrees; they’re ideal for complex rafter angles. Most of this added ability will be lost on the non-specialist, but if you use a circular saw a lot, you can use a rafter square as a saw guide for making consistently straight 90-degree cuts (see this image). If you’re getting interested in advanced carpentry, you can learn more about the nearly infinite uses of a rafter square in this booklet, which comes with Irwin’s version of the tool.
For any kind of woodworking or carpentry, we recommend picking up an Irwin 1794469 12-inch Combination Square (about $11). Compared with other similarly priced squares, the Irwin has a much better build quality, and it even rivals some more expensive options. If the Irwin is unavailable, try the Swanson 12-inch Combo Square (about $9). It will save you a few bucks, but it’s nowhere near as polished.
The key's under the mat.