How to Measure Screws and Bolts

Make sure you use the right size of screw or bolt for your project.

When a job calls for a specific size screw or bolt, most people start rummaging through their tool box or coffee cans of odd screws, nails and sundry items. Knowing how to accurately measure those screws and bolts will save you time and the trouble of mistakes in your projects. When you measure screws and bolts, you're measuring the part of the fastener that will go inside the surface you're putting it into. Most are measured from the bottom of the head down to the tip.

Things You'll Need

• Ruler or stiff tape measure

Instructions

1. Measure round head screws from directly under the head to the tip. Place the end of the ruler or tape measure so that it touches the underside of the screw head and measure down from there to the end.

2. Measure flat countersunk screws from the top of the screw to the tip. These will be flush with the surface when they're screwed in.

3. Measure an oval head countersunk screw from the widest part of the head to the tip. This means that you're measuring it as if it were a flat head and you're disregarding the rounded top. All screws -- machine, wood and sheet metal as well as all bolts -- are measured this way.

4. Measure eye bolts from directly under the eye to the tip. If the eye bolt has a little lip or projection under the head, measure it from right under that. Hangar bolts are measured from the top to the end.

References

• Bolt Depot: How Fasteners Are Identified
• Nuts and Bolts: How to Measure a Bolt