How Accurate Should a Straight Edge Be?

Last updated 11 November 2026

Buy the accuracy the job needs, not the most impressive number. For rough layout, a rule with no stated straightness is often fine. For dependable marking, cutting and practical checks, choose a straight edge with a published workshop tolerance, such as Maun’s 0.001 inch per foot (0.084 mm per metre). For formal inspection, calibration or recorded results, specify the correct DIN 874 grade with a certificate.

Quick guide: how much accuracy do you need?

Start with the consequence of error

Before you compare numbers, ask what a small error would actually cost you:

• Cosmetic variation: a line that’s a fraction out but nobody will notice.
• Wasted stock: a mis-cut panel, hide or sheet.
• Failed assembly: parts that don’t line up or seal properly.
• Invalid inspection: a quality decision you can’t back up.

The higher the cost of being wrong, the more evidence of accuracy you need.

No specification: what a rule doesn’t tell you

A rule can measure length accurately and still give no assurance that its edge is straight. Graduations are printed or etched to their own tolerance; edge straightness is a separate property. If the supplier publishes no straightness figure, the straightness is simply unknown. That doesn’t make the rule inaccurate: it means you have no evidence either way.

A published workshop tolerance: what Maun’s figure means

Maun steel and aluminium safety straight edges have a bevelled working edge accurate to 0.001 inch per foot (0.084 mm per metre). In plain terms:

• Over 1 metre, the edge stays within 0.084 mm of true: less than a tenth of a millimetre.
• Over 500 mm, it stays within 0.042 mm.
• Over 2 metres, it stays within 0.168 mm.
• Over 12 inches, it stays within 0.001 inch.

That’s a known, useful tolerance for scribing, marking, cutting and scoring, and for practical checks for visible bow or misalignment. It gives you confidence that the line is right, without paying for inspection-grade equipment.

DIN 874: grades, not a single number

DIN 874 is a German standard for straight edges used in inspection. It defines accuracy grades, 00, 0, 1 and 2, with 00 the most precise, and the permitted deviation for each grade depends on the length of the straight edge. So “DIN 874” on its own doesn’t tell you how accurate a tool is. Always check the grade, the length and the cross-section.

Specialist suppliers such as Messmittel.tools, K-MET (formerly Kinex) and Limit offer DIN 874 straight edges for straightness and flatness inspection. These typically have heavier sections and protected measuring faces, and certificates or calibration may be included or offered as an option.

The cost of accuracy

Price rises with each step up in certainty:

• Generic rule: lowest cost, no straightness evidence.
• Workshop straight edge with a published tolerance: a modest step up for known, dependable accuracy.
• DIN 874 grade 2: a defined inspection grade.
• DIN 874 grades 1 and 0: tighter tolerances, higher prices.
• DIN 874 grade 00 and knife-edge straight edges: the most precise, and the most expensive.

When Maun is the right choice

Choose a Maun straight edge when you need a known, useful tolerance and a robust working edge, but you don’t need a calibration certificate or inspection-grade accuracy. That covers most fabrication, maintenance, leatherwork, sign making, flooring, glazing and craft work.

When you need more than Maun offers

Choose a DIN 874 straight edge for quality sign-off, calibration, machine-tool inspection or any result you must measure, record and defend. A Maun straight edge is a workshop tool, not calibrated metrology equipment.

Accuracy in use

Even the best edge can only be as accurate as the way it’s used. These can easily outweigh the published figure:

• Dirt and swarf under the edge or on the work.
• Burrs and edge damage from knocks or careless storage.
• Temperature differences between the tool and the work.
• Support: a long edge resting on uneven points.
• Pressure: pressing too hard can flex the edge or the work.

Keep the working edge clean, store it hanging from its hole, and handle it with care.

Which accuracy should you buy?

Buy a standard rule when a small error doesn’t matter. Buy a Maun straight edge when you need specified workshop accuracy to protect your material and your time. Buy the right DIN 874 grade when the result has to be inspected, recorded or certified.

Compare Maun steel straight edges or compare Maun aluminium safety straight edges.

Frequently asked questions

How accurate is a Maun straight edge?

The bevelled working edge of every Maun steel and aluminium safety straight edge is accurate to 0.001 inch per foot (0.084 mm per metre). Over a full metre, that’s within 0.084 mm of true.

Is 0.084 mm per metre accurate enough for engineering?

For marking out, scribing, fabrication, assembly, maintenance and practical straightness checks, yes. For machine-tool inspection, calibration or formal flatness verification, you need a calibrated DIN 874 straight edge.

What do DIN 874 grades mean?

DIN 874 sets accuracy grades for inspection straight edges: 00, 0, 1 and 2, with 00 the most precise. The permitted deviation for each grade increases with length, so always check the grade and length together.

Is a Maun straight edge DIN 874 certified?

No. Maun straight edges are workshop tools with a published accuracy of 0.001 inch per foot (0.084 mm per metre). They are not DIN 874 graded or supplied with a calibration certificate.

Does a ruler have a straightness tolerance?

Usually not. Most rules specify the accuracy of their graduations but say nothing about the straightness of the edge. If no figure is published, treat the straightness as unspecified.

What affects the accuracy of a straight edge in use?

Dirt, burrs, edge damage, temperature, poor support and too much pressure. A clean, well-stored edge used with a light, steady touch will perform to its specification.