How to Use a Ruler

A complete beginner’s guide to using a ruler for accurate measuring, marking, layout, and field use. Learn how to read, use, and master a ruler from scratch.

What a Ruler Is

A ruler is a measuring and layout tool used to mark straight lines, measure distances, make accurate cuts, and create repeatable spacing. At Grim Workshop, our rulers are built into Survival Cards, Dog Tag Tools, Micro Tools, and other flatpack gear so you always have a measuring instrument with you — even when you're miles from a toolbox.

Whether you’re building, repairing, making gear, cutting cordage, or doing fieldcraft, a ruler makes your work safer, cleaner, and more accurate. Measuring wrong leads to broken parts, bad fits, wasted materials, and gear failures. Measuring right prevents all of that.

This guide teaches you how to fully understand and use a ruler, even if you’ve never measured anything in your life.

→ All Items with a ruler

Why Rulers Matter in EDC and Survival

Accuracy Saves Time and Materials

If you only “eyeball” everything, you waste materials and risk gear failures.

Clean Layouts = Clean Results

Everything looks and works better when the cuts and marks are precise.

They Help You Reproduce Results

You can’t rebuild, repair, or repeat something if you don’t measure it consistently.

Essential for Field Repairs

Sewing patches, cutting cordage, replacing straps, repairing tarps — all require measuring.

Built Into Many Grim Tools

You always have a ruler available because it’s built directly onto flatpack Survival Cards and Micro Tools.

How to Read a Ruler

Understanding Inches

Most rulers have inch marks broken into fractions:

Whole inches
1/2 inch
1/4 inch
1/8 inch
1/16 inch

The smaller the line, the smaller the fraction.

Understanding Millimeters and Centimeters

Metric uses:

Millimeters (mm) — smallest marks
Centimeters (cm) — larger numbered marks

Metric is simpler because everything is base 10.

Which Is Better?

Inches are common in carpentry and US-made gear.
Metric is common in precision tools, knives, bushcraft gear, and outdoor equipment.

Grim’s rulers often include both because versatility matters.

How to Use a Ruler for Measuring

Step 1: Align the Zero Point

Most rulers start at the very edge.
On some tools, “0” starts slightly inward. Know which version you have.

Step 2: Place the Edge of the Ruler Exactly on the Starting Point

Do not angle the ruler.
If the ruler isn’t flat and straight, your measurement is wrong.

Step 3: Look Directly Over the Ruler

Looking from an angle causes “parallax error,” making measurements appear shorter or longer.

Step 4: Read the Mark at the End Point

Use the smallest lines available for the most accuracy.

Step 5: Double Check

Measure twice, cut once.

This rule is as old as tools themselves — for good reason.

Using a Ruler to Mark Straight Lines

Step 1: Hold the Ruler Firmly

If it moves while you draw, the line is off.

Step 2: Place Your Pencil or Marker at the Starting Point

Use the ruler edge as your guide.

Step 3: Draw Slowly Along the Edge

Speed = crookedness.

Step 4: Check Your Line

If it wavers or lifted from the ruler, redraw.

A straight line is the foundation of precise cutting, folding, building, stitching, and shaping.

Using a Ruler to Measure Curves, Gear, and Irregular Shapes

Measuring Curves

Use flexible tools or:

Lay cordage along the curve.
Mark the length on the cord.
Measure the cord with your ruler.

Measuring Cylinders

Roll the cylinder on the ruler until it completes one full turn — that gives circumference.

Measuring Gear Thickness

Stand the ruler upright next to the object.

Measuring Depth

Lower the ruler edge-first into the item until it hits bottom.

How to Convert Between Units Using a Ruler

Inches to Metric

1 inch = 2.54 centimeters
½ inch = 1.27 centimeters
¼ inch = 0.635 centimeters

Metric to Inches

1 centimeter ≈ 0.39 inches
10 mm = 1 cm
25.4 mm = 1 inch

Your ruler makes all of this easier because you can directly compare the two scales.

How to Use a Ruler for Field Repairs

Cutting Cordage to Exact Lengths

This prevents wasted rope and ensures equal lengths for lashing, shelters, snares, or sewing.

Sizing Patches and Fabric

A ruler ensures your repair patches match the damage exactly.

Spacing Stitch Holes

Even spacing makes field repairs stronger and cleaner.

Replacing Straps

Measure before you cut so new straps match the original.

Planning Campcraft Projects

Tripod legs, pot hangers, tarp tie-outs — all benefit from consistent lengths.

Advanced Ruler Techniques

Using Rulers for Angles

Some rulers include a square corner or angle marks.
If not, you can create a 90 degree corner using:

The corner of a book
A card with square corners
Any straight edge combined with your ruler

Using Rulers as Straightedges

You can:

Guide knife cuts
Align gear on flat surfaces
Keep lashings straight
Make perfectly straight folds

Measuring Internals

Insert the ruler into:

Containers
Slots
Gaps
Channels

Then mark the depth with your thumb and read the measurement outside.

Improvised Rulers

(Fast + Surprisingly Accurate)

1. Your Thumb Width = About 1 Inch

Most adults have a thumb that’s roughly one inch across at the knuckle.
(If yours is wildly different… congratulations, you’re special.)

2. Your Fingertip to First Knuckle = About 1 Inch

The pad of your index finger (top segment) is almost always right at an inch long.

3. Your Hand Width Across Knuckles = About 4 Inches

Make a fist. Measure across the knuckles. This is consistently close to 4 inches on most adults.

4. Your Hand Span (Thumb Tip to Pinky Tip) = About 8 to 9 Inches

Spread your hand wide. Thumb to pinky tip is usually around 8.5 inches for most people.

5. Your Palm (Top to Bottom) = About 4 Inches

From the base of the palm to the start of the fingers.

6. Your Forearm (Elbow to Wrist) = About 10 to 12 Inches

This varies more than the others, but it’s a decent estimate when you need a quick foot-long measurement.

7. Your Foot = About 10 to 12 Inches

Most adult shoes are around this size. Good for measuring “about a foot” in the field.

8. Pace Length (One Natural Step) = About 2.5 Feet

This is great for measuring:

Campsites
Path distances
Survival shelters
Ropes and cordage

Two steps ≈ 5 feet.
Four steps ≈ 10 feet.

Object-Based Measurements (When Body Parts Won’t Cut It)

9. Dollar Bill = Exactly 6.14 Inches Long and 2.61 Inches Tall

If you're carrying cash, you’ve got a tiny ruler.

10. Credit Card = 3.37 Inches Long

Exactly the same size worldwide.

11. Standard Key = About 2.25 Inches Long

Surprisingly useful for quick measuring.

12. Standard Pen = About 5.5 to 6 Inches

Most disposable pens fall between those two numbers.

13. Paracord Inner Strands = Roughly 1mm Each

Helpful when making precise knots or spacing lashings.

14. A Sheet of Paper (Letter Size) = 11 x 8.5 Inches

Folding paper into halves gives predictable lengths:

Half sheet: 5.5 inches
Quarter sheet: 2.75 inches

15. A Standard Bic Lighter = About 3 Inches Tall

Everyone at camp seems to have one.

EDC/Survival Situational Tricks

16. Wrap Method for Measuring Rope or Cord

Wrap cordage around your elbow and palm:

1 wrap = roughly 1.5 to 2 feet
5 wraps = about 8 to 10 feet
Great for quick shelter-building measurements.

17. Measuring With Knots

Tie knots at equal spacing along paracord (for example, every thumb width).
Now you have a flexible measuring device forever.

18. Knife Blade Measurement

If you know your blade length (like many people do), you can stack it along the object to estimate length.

FAQ

Q: Why do I need a ruler in the field?
A: Accurate measurements prevent wasted materials and make repairs stronger and cleaner.

Q: Are Grim Workshop rulers accurate even though they’re small?
A: Yes. They are precision-cut and identical to full size marks, just in a smaller format.

Q: Can I still measure big objects with a small ruler?
A: Yes. Measure in sections or mark distances repeatedly.

Q: How do I measure curves or round objects?
A: Use cordage to map the curve, then measure the cord with your ruler.

Q: Does it matter if I use inches or metric?
A: Both are valid. Inches are common in US repairs. Metric is better for precision.

Q: Why do my measurements sometimes seem off?
A: Parallax — looking from an angle instead of directly above the ruler.

Q: What if my ruler’s zero starts a little inward?
A: Align the first mark with the starting point instead of the ruler’s edge.

Q: Can rulers guide cutting tools?
A: Yes, but use caution. Thin rulers can slip if pushed too hard.

Q: Can rulers bend? Does that ruin accuracy?
A: Slight flexibility is fine. Permanent bends compromise accuracy.

Q: Can I use a ruler to check alignment?
A: Yes. The straight edge works like a mini level for layout and spacing.

Q: What if my ruler doesn’t reach far enough?
A: Take multiple measurements and add them together.

Q: Do rulers help with sewing repairs?
A: Absolutely. They space stitches evenly and cut patches to size.

Q: Can rulers be used in the dark?
A: Yes with a glow card, flashlight, or marking your ruler beforehand.