How to Measure Odd Shapes with a Double Sided Tape Measure

Quick answer

To measure an odd shape, break it into straight segments and use the tape's bottom edge to follow curves. For true curves, wrap a flexible tape or use a contour gauge, then measure that. The double sided tape measure helps because you can read the top scale while the bottom edge stays aligned against the shape.

Measuring a curved object or an irregular shape with a standard tape measure usually ends with a squinted eye and a guess. The blade slips, the hook can't grab, and the number you read is rarely the number you need. A double sided tape measure solves part of that problem by giving you a reading on both edges, but you still need a repeatable method.

This guide walks through a practical sequence for measuring odd shapes, from simple curves to complex profiles. You'll also see where a tape measure stops being the right tool and which Excel Blades products can help when it does.

Why odd shapes are hard to measure

A tape measure is designed for straight lines. Its hook catches an edge, the blade extends flat, and the markings assume the surface is flat and rigid. Curved objects break all three assumptions. The blade bridges across a concave curve instead of following it, and on a convex curve the blade lifts away from the surface.

Double sided tape measures add a second scale on the bottom edge, which lets you read a measurement without flipping the tape. That helps when you're working around a shape and can't see the top face, but it doesn't make the blade flexible. You still need a strategy for capturing the shape before you measure it.

• Check that the tape's hook is not bent; a damaged hook adds error to every measurement.
• For repeat work, write down your method so the next measurement matches.

Step-by-step: measuring curved and irregular objects

Start by deciding whether you need a straight-line distance or a true surface length. A straight-line distance is the shortest path between two points, like the diameter of a bowl. A true surface length follows the curve, like the distance around the rim. Mixing these up is the most common mistake.

For straight-line distances, lay the tape across the object and read the top scale. For surface lengths, wrap a flexible measuring tape or a strip of paper around the curve, mark where the ends meet, then lay that strip flat against your double sided tape measure. The bottom scale lets you read the strip without twisting it.

For complex profiles, use a contour gauge to copy the shape, then trace it onto paper and measure the trace. If the object has internal corners, measure each straight segment separately and add them rather than trying to bend the blade into the corner.

• Keep the tape perpendicular to the edge you're measuring from; an angled tape reads long.
• Mark your start point with a pencil or a piece of painter's tape so you can repeat the measurement.

Using the double sided scale to your advantage

The second scale on a double sided tape measure is most useful when the object blocks your view of the top edge. For example, when measuring inside a drawer or around a pipe, you can read the bottom scale while the top scale faces away. This reduces the need to reposition the tape, which is where errors creep in.

When you use the bottom scale, confirm which direction the numbers run. Some tapes have the bottom scale running in the opposite direction, which is handy for subtracting from a reference point but confusing if you forget. Do a quick test on a known length, like a piece of paper, before you trust the reading.

• Use the bottom scale for inside measurements where the hook cannot reach.
• If the bottom scale runs opposite, note it on your sketch to avoid sign errors.

When a tape measure is not enough

Some shapes are better measured with a dedicated tool. A jeweler's saw blade, for instance, is not a measuring tool, but its fine teeth let you cut a template of a complex curve so you can measure the template flat. Similarly, a machinist square checks whether two edges are truly perpendicular before you measure, which prevents you from measuring a shape that is already out of square.

If you frequently measure small, deep holes or need to transfer a measurement to a drill, a drill bit set can help you create a pilot hole at the marked center. The tape measure gets you close; the right accessory gets you exact.

• Use a square to verify corners before measuring; otherwise your measurements inherit the error.
• For small parts, measure in millimeters to avoid fractions.

Step-by-step: measure an odd shape

1. Identify the measurement type: Decide if you need a straight-line distance (e.g., diameter) or a surface length (e.g., circumference). This choice determines whether you can use the tape directly or need a flexible aid. Checkpoint: write down 'straight' or 'surface' before you start.
2. Stabilize the start point: Place the tape's hook against a firm edge, or mark a start line with tape if there is no edge. For curved surfaces, hold the tape so it does not slide. Mistake to avoid: letting the hook float on a curve; it will shift and add error.
3. Capture the curve with a flexible aid: Wrap a strip of paper or a flexible tape around the curve, mark the overlap, then lay it flat against your double sided tape measure. Read the bottom scale if the top is blocked. Checkpoint: verify the strip is not twisted; a twist reads long.
4. Measure straight segments separately: For shapes with corners, measure each straight run individually and add them. Do not try to bend the tape around a corner. Mistake to avoid: measuring across a corner instead of along each edge.
5. Verify with a second method: Re-measure using a different approach, such as a contour gauge or a template cut with a fine saw. Compare the numbers. Checkpoint: if the two readings differ by more than 1/16 inch, find the cause before cutting.
6. Record and transfer the measurement: Write the final number on your sketch, noting which scale you used. If drilling, mark the center point and use a micro drill bit for a pilot hole. Next step: test-fit on scrap material before committing to the final piece.

Tools that help with odd-shape measuring

• 8" Machinist Square: Excel Blades 8" Machinist Square is a high-precision measuring tool designed for engineers, machinists, woodworkers, and metalworkers who require accurate 90° angles. Before you measure an odd shape, check that its reference edges are square. If they are not, your tape measurement will be off, and this square tells you immediately.
• #2/0 Jewelers Saw Replacement Blades - 64 Teeth/Inch: The Excel Blades #2/0 Super Fine Piercing Saw blade is a light weight saw blade crafted for projects that clearly require more power and precision than most saw blades you will find at a tool shop. When a curve is too complex to measure directly, cut a thin template with this blade, then measure the template flat with your double sided tape measure.
• 12-Piece Assorted Drill Bit Set: Excel Blades 12-Piece Assorted Drill Bit Set (#55521) delivers precision in a compact package. This fine high-speed steel set includes drills #60 through #70, ideal for crafting detailed holes in materials such as wood, resin, beads, jewelry, walnut. After you mark a center point from your measurement, these micro drill bits let you drill a precise pilot hole without wandering, so the final hole matches your measurement.

Measuring odd shapes gets easier when you stop forcing the tape to do everything. Use the double sided scale to read around obstacles, break curves into segments, and bring in a square or a fine saw when the shape refuses to cooperate. A few extra seconds of setup saves a ruined cut.