Square, spirit level, tape measure: choosing the right measuring tools

A shelf that leans, a cut that isn't square, a flat-pack unit that no longer closes: in DIY, most mistakes come from a measurement or a marked line, not from the saw. A few well-chosen measuring and marking tools are all you need to work accurately, provided you know what each one is for.

The tape measure: length above all

It is the tool you reach for most often, and the one that most often falls off the stepladder. Three points make the difference:

The length of the tape: 3 to 5 m is enough for a piece of furniture; for a room, a wall or a floor, a 10 m tape saves you measuring in two goes and adding up errors.
A rigid steel blade stays straight when extended unsupported: you can measure a ceiling height or a window width on your own, without the tape sagging.
A reinforced case and a locking button: the case absorbs drops, and the lock holds the tape while you read or mark.

The small hook at the end of the tape moves slightly: on most tape measures, this play makes up for its own thickness, whether you hook it over the edge of a board or push it against a wall. Don't tighten it.

The square: truly right angles

There are several kinds, each for a specific task:

The try square: its thick stock sits flat against the edge of the board, and the blade marks a perpendicular line. It is the basic tool for cutting straight and checking a joint.
The triangular rafter square: a single piece, with no adjustment, that marks at 90° and 45°. Handy for battens, skirting boards and mitre cuts.
The marking square with holes: you slip the pencil tip into a hole and slide it along the edge to draw a line parallel to the edge, always at the same distance.
The sliding-stock marking rule: a sliding stock rests against the workpiece and the rule marks at 90°, 45° or 60° depending on the setting.

To check that a square is accurate, draw a line along its blade, flip it over and draw again from the same point: if the two lines coincide, the angle is a right angle.

The spirit level: horizontal, vertical and 45°

Several vials: one for horizontal (shelf, curtain rail), one for vertical (upright, door frame), sometimes one at 45°.
A thick aluminium body resists twisting. A warped level gives a false reading without you noticing.
A perfectly flat contact face: this is the side that touches the surface, and it must bear along its whole length.

The check takes two seconds: set the level down, note the position of the bubble, then turn it end to end in the same spot. The bubble should return to exactly the same place.

Taking and transferring an angle

A wall is almost never perfectly square. To fit a shelf into a corner or a skirting board against an out-of-true wall:

The sliding bevel angle finder with its pivoting arm takes the existing angle, locks with a screw and transfers it exactly onto the piece to be cut, without reading a single figure.
The protractor gives the value in degrees; in stainless steel with engraved graduations, it stays legible far longer than a printed plastic one.

Reading a scale drawing

The triangular scale ruler carries several reduction scales on its three faces: you lay down the face that matches the scale of the drawing and read the real dimension directly, with no calculation. Useful for a kitchen plan, a fit-out plan or a house plan.

Good habits for accurate marking

Measure twice, cut once: always re-read the dimension before cutting.
Stick with the same tape measure from start to finish of a project: two different tools may not give quite the same measurement.
Mark finely: a well-sharpened pencil or a scriber, and cut on the waste side of the line.
Press the stock firmly against the edge before marking: it is the stock that guarantees the angle, not your hand.

Care

Wipe the tape measure blade if it has got wet or dusty before letting it retract.
Store squares and levels flat or hanging up: a measuring tool that gets knocked about in a box ends up losing its accuracy.
Never use a level or a square as a lever or a hammer.

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