Mitre Squares

About Mitre Squares

A mitre square is an essential precision tool used by carpenters, joiners, and woodworkers to mark and verify accurate 45-degree angles for mitre joints. Unlike adjustable angle finders, a mitre square is fixed at precisely 45 degrees, making it the go-to tool for quickly checking and marking corners for picture frames, skirting boards, architraves, and other decorative mouldings. The fixed angle design ensures consistent, reliable measurements without the risk of adjustment drift that can occur with variable angle tools.

Traditional mitre squares typically feature a robust blade attached to a handle, often made from hardwood, aluminium, or composite materials. The blade is permanently set at 45 degrees to the handle, allowing tradespeople to quickly check internal and external mitres with confidence. Modern designs have evolved to include innovative features, such as the Hultafors mitre square available from Tooled-Up.com, which automatically calculates the correct cutting angle without manual calculations. This type of tool uses an indicator flag that divides angles by two, eliminating errors and speeding up the marking process on site.

Whether you're fitting crown moulding, constructing picture frames, or installing dado rails, a quality mitre square delivers the speed and accuracy that professional joiners demand. The simple, robust design means there are no moving parts to fail, no adjustments to slip, and no batteries to charge—just reliable angle measurement every time you reach for it. For tradespeople working on period properties, shop fitting projects, or fine furniture construction, a mitre square remains an indispensable part of the toolkit.

Jargon Buster

• 45-Degree Angle: The standard angle for mitre joints, where two pieces of material meet at a corner to form a 90-degree right angle. Each piece is cut at 45 degrees so they fit together perfectly.
• Mitre Joint: A joint made by cutting two pieces of material at complementary angles (typically 45 degrees each) so they meet to form a corner, commonly used in picture frames, skirting boards, and architectural mouldings.
• Internal Mitre: An inside corner joint, such as where two walls meet, requiring precise 45-degree cuts for professional results.
• External Mitre: An outside corner joint, such as the corner of a skirting board running around a chimney breast.
• Indicator Flag: A moveable marker on adjustable mitre squares that automatically calculates the correct cutting angle by dividing the measured angle by two, eliminating manual calculations.
• True Square: A term describing when a tool has been manufactured to exact specifications with minimal tolerance for error, ensuring accurate marking and measurement.

Who Uses Mitre Squares?

Mitre squares are indispensable tools for a wide range of trades and applications:

• Carpenters and Joiners: For fitting skirting boards, architraves, picture rails, dado rails, and creating precise mitre joints in furniture construction
• Cabinet Makers: Essential for producing accurate corner joints in fine furniture and bespoke cabinetry
• Picture Framers: Critical for creating perfect 45-degree corners that ensure frames hang square and look professional
• Shop Fitters: For installing decorative mouldings and trim work in retail and commercial spaces
• General Builders: Useful when installing crown moulding, coving, and other decorative elements
• DIY Enthusiasts: Home improvers tackling skirting board replacement, architrave fitting, or building their own picture frames
• Restorers: Period property specialists working on historic mouldings and decorative woodwork

How to Choose the Right Mitre Squares

Selecting the appropriate mitre square depends on several key factors:

Traditional vs. Automatic: Fixed traditional mitre squares offer simplicity and reliability with no moving parts, whilst automatic angle-dividing models like those from Hultafors eliminate calculation errors and speed up marking tasks. Consider whether you need the additional functionality of automatic angle calculation for complex projects or prefer the straightforward nature of a fixed 45-degree tool.

Build Quality and Materials: Look for mitre squares with durable blades and robust handles. Fibreglass-reinforced nylon offers excellent durability and is lighter than metal alternatives, whilst stainless steel blades resist corrosion. The handle should be robust—hardwood and aluminium handles offer excellent durability on site, whilst composite materials provide strength with reduced weight.

Size and Portability: Consider the typical dimensions of the materials you work with. A 150mm mitre square is compact and portable, ideal for site work and fitting into toolboxes. Larger models provide more reference surface for checking bigger workpieces but sacrifice portability.

Accuracy and Tolerances: Professional-grade mitre squares are manufactured to tight tolerances, essential for high-quality joinery where even minor deviations become visible in the finished work. Established brands like Hultafors are renowned for their precision engineering and long-lasting construction.

Ergonomics: The handle design affects comfort during extended use. Look for contoured or textured handles that provide a secure grip, particularly important when working with gloves or in dusty conditions on site.

Versatility: Some modern mitre squares can measure both internal and external angles, offering greater flexibility for various joinery tasks. Models with indicator flags that divide angles automatically are particularly useful for complex crown moulding and architectural work where non-standard angles are encountered.

Popular Accessories

To get the most from your mitre square, consider these complementary tools and accessories available at Tooled-Up:

• Mitre Saws: Once you've marked your angles, a quality mitre saw or chop saw from brands like Makita, DeWalt, or Bosch cuts the material accurately to your marked lines
• Combination Squares: Pair your mitre square with a combination square for checking 90-degree angles and general marking tasks
• Marking Tools: Sharp carpenters' pencils or marking knives create precise lines when used with your mitre square
• Bench Hooks: Secure workpieces whilst marking and cutting mitre joints for safer, more accurate results
• Spirit Levels: Ensure your mitre cuts are plumb and level when fitting skirting boards and mouldings
• Try Squares: Complement your mitre square with try squares from Stanley or Bahco for standard 90-degree marking operations
• Tool Storage: Protect your precision tools during transport with Stanley FatMax, DeWalt TSTAK, or Milwaukee PACKOUT storage systems

Frequently Asked Questions

Can I use a mitre square for angles other than 45 degrees?
Traditional fixed mitre squares are specifically designed for 45-degree angles only. However, automatic mitre squares with indicator flags, such as the Hultafors model, can measure any angle and automatically calculate the correct cutting angle by dividing it by two, making them suitable for both standard and non-standard mitre work.

How do I check if my mitre square is still accurate?
For fixed mitre squares, mark a 45-degree line along a straight edge of a piece of timber, then flip the tool over and mark from the opposite side. If both lines align perfectly, your mitre square is accurate. Any discrepancy indicates the tool is out of square and should be replaced, as fixed mitre squares cannot typically be adjusted.

What's the difference between a mitre square and a combination square?
A mitre square is dedicated specifically to marking and checking mitre angles. A combination square features a moveable head that typically includes 90-degree and 45-degree faces, plus additional functionality like depth gauging and spirit levels, making it more versatile but potentially less specialised for repeated mitre work.

Do I need a mitre square if I have a mitre saw with preset angles?
Yes, a mitre square remains valuable for marking workpieces before cutting, checking the accuracy of your saw's preset angles, and verifying joints after assembly. It's also essential for scribing mitres directly onto installed work where a saw cannot be used to check angles, such as when fitting skirting to existing architraves.

Are fibreglass-reinforced nylon mitre squares as accurate as metal ones?
Modern fibreglass-reinforced nylon mitre squares from reputable manufacturers like Hultafors are manufactured to professional tolerances and offer excellent accuracy. They provide the advantage of being lighter and more resistant to corrosion than some metal alternatives, whilst maintaining the precision required for professional joinery work.