What's inside
As an Amazon Associate I earn from qualifying purchases. This post may contain affiliate links at no extra cost to you.
What Each Square Actually Is
A try square is a carpenter’s square. It has a thick wooden or plastic stock and a thinner steel blade riveted at 90 degrees. The stock is thick so you can register it against the edge of a board and scribe a line across the face. Good ones are around 6 to 12 inches long. Most of the accuracy comes from how well that blade is set into the stock at the factory, and that joint is vulnerable to knocks, drops, and seasonal wood movement if the stock is timber.
An engineers square is an all-steel square, usually hardened and ground. Blade and stock are one piece of steel or a ground blade fixed into a heavy, machined stock with no adjustment. Sizes are typically 2 to 6 inches for workshop use, with 4 inch and 6 inch being the most useful for mitre saw work. There is no marking function, the thick stock is just a reference face. You buy it for checking, not for marking.
The important difference is not the look, it is how they are made and inspected. A try square is made to be good enough for joinery layout. An engineers square is made to a standard.
Accuracy and Tolerances That Matter
Numbers help here. Most decent try squares are specified as something like 0.5mm deviation over 300mm, if they are specified at all. Many budget try squares are worse and are not checked after assembly. You can test this yourself: mark a line against the square, flip it over, and mark again from the same edge. If the lines diverge, the square is out. It is common to see 0.3 to 0.8mm of error on a 200mm try square after a year on site.
Engineers squares are graded. Under DIN 875, Grade 2 allows about 0.02mm deviation over 100mm, Grade 1 about 0.01mm, and Grade 0 even less. A good 100mm (4 inch) Grade 1 engineers square will show no light under the blade when held against a true straight edge, and will be well within 0.02mm over its full length. That is roughly 20 to 40 times more accurate than a typical try square.
For mitre saw setup, that matters because saw errors stack. If your square is 0.5mm out over 150mm and you use it to set the blade to 90 degrees, your cut will be 0.19 degrees out before you even start cutting. Over a 250mm wide board, that is a 0.8mm gap in a mitred joint or a visible step in a casing mitre. An engineers square keeps that initial error under 0.01 degrees, which is effectively perfect for woodwork.
| Feature | Try Square | Engineers Square |
|---|---|---|
| Construction | Steel blade in wood, plastic or aluminium stock | Hardened, ground solid steel blade and stock |
| Typical accuracy | 0.3 – 0.8mm over 150-300mm, often unspecified | 0.01 – 0.02mm over 100-150mm (DIN 875 Grade 1/2) |
| Common sizes | 150mm, 200mm, 300mm (6″, 8″, 12″) | 50mm, 75mm, 100mm, 150mm (2″, 3″, 4″, 6″) |
| Failure mode | Blade loosens, stock dents, timber moves with humidity | Still accurate after drops unless burr raises on edge, can rust if not oiled |
| Best use on mitre saw | Quick check that fence and table look square, marking stock | Setting 90 degree and 45 degree blade tilt accurately |
| Price range | $15 – $50 | $25 – $70 for Grade 1, 100-150mm |
Using Them on a Mitre Saw
Verifying a mitre saw is really two checks: blade to table for square cuts, and blade to fence for mitres. The fence check is where squares get misused.
For blade to table (the bevel or tilt), an engineers square 100mm is the right tool. Unplug the saw, raise the blade guard, and put the stock flat on the table with the blade vertical. Slide the blade of the square up against the saw plate, not the teeth. Sight for light between the square and the plate. You need to check in two places: close to the table and higher up the blade, then rotate the square to the other side of the blade and check again. If you see a wedge of light, adjust the 90-degree stop. A try square is too tall and too coarse here; its blade flexes and its stock often does not sit flat on a mitre saw table because of the throat plate gap.
For blade to fence (the mitre angle), neither square is ideal without help. Most mitre saw fences are not perfectly flat or continuous, and a 100mm engineers square is too short to span fence imperfections. A 150mm engineers square or a known-good large try square can bridge that better, but for true 90 degrees to the fence you are better off making a test cut and checking the offcut. Cut a board about 200mm wide, flip one half over, and butt the cut ends together against the fence. Any error doubles and shows as a gap. An engineers square can then tell you if the gap is the square or the saw.
The other common check is 45 degrees. Do not use a try square for this. A try square only has 90 degrees. A combination square or a dedicated 45 degree engineers square is needed if you want to set the bevel to 45 degrees without a test cut. Even then, trust the cut more than the gauge. Set to 45, cut two scraps, put them together to make 90 degrees and check that outside corner with your engineers square.
Durability and Site Realities
On site, a try square lives in a tool belt or tote, gets knocked, gets wet, and still gets used for marking. That is what it is for. You can replace it cheaply and you will not cry if it falls off a sawhorse. The wooden stock will eventually move, and the rivets can loosen. Check it with the flip test weekly if you care about it.
An engineers square does not like site life. It will keep its accuracy if you keep it in its case and keep rust off it, but drop it on concrete and you can raise a burr on the stock or blade edge that makes it read out. That burr can be stoned off, but most people do not. It is also too small and sharp to mark with comfortably. Treat it as an inspection tool that lives in a drawer, not a layout tool. For that reason many carpenters own both: a try square 8 inch for everyday marking and an engineers square for machine setup.
If you only work with site timber, MDF, and framing, the tolerance of a decent try square is often acceptable and you will correct errors with swipes of a hand plane anyway. If you cut pre-finished mitres, hardwoods, or large crown moulding where a gap cannot be filled, the engineers square pays for itself in one avoided re-cut.
Which Should You Buy for Mitre Saw Setup
Buy on accuracy needs, not prestige.
If you have one square and cut mostly studwork, skirting, and general carpentry, keep a good try square and learn to verify it. Spend $30 to $40 on one with a thick aluminium or hardwood stock that holds its blade well, and do the flip test before you set your saw. It will get you within 0.5mm on most cuts, which putty and caulk will hide.
If you set up a mitre saw for finish work and want cuts that close without filler, get a 100mm or 150mm DIN 875 Grade 1 engineers square and keep it separate from site kit. It is the simplest, cheapest way to know your 90 degree stop is actually 90 degrees. You do not need a matched set or a Grade 0 square. A single DIN 875 Grade 1 engineers square in 100mm or 150mm will cover bevel checks and doubled-up mitre checks for years.
Avoid large, cheap stainless engineers squares sold without a grade. They are often just try squares made from steel and are no more accurate than a $20 try square, but they look precise. If the listing does not mention DIN 875 or BS 939 and give a grade, assume it is not graded.
A Practical Verification Routine
Use this order, it takes three minutes.
Clean the table and fence. Lower the blade to cutting depth and lock at 0 degrees mitre and 0 degrees bevel. Put your engineers square stock on the table and check blade to table on both sides of the blade with no light showing. Adjust the stop if needed, then lock and re-check.
Then cut a test piece. Take a straight, flat scrap at least 200mm wide and 300mm long. Crosscut it at 90 degrees, flip one offcut over, and hold the two cut faces together on the table. Hold your engineers square against the joint. If there is a gap at the top or bottom, your fence-to-blade is off. Adjust the mitre detent, not the square.
For 45 degrees, cut two scraps at 45, put them together to form a 90-degree corner, and check that corner with the engineers square. If the corner is not 90, split the error and adjust the bevel stop half the gap. Two test cuts will get you tighter than any gauge alone, and the engineers square just tells you objectively whether the combined cut is square.