Selecting proper screw sizes makes the difference between a wobbly shelf and a sturdy installation.

This Standard Screw Sizes Chart 2025 clarifies metric and imperial measurements, explores common screw types, and simplifies matching fasteners to materials. 

Understanding Screw Sizes: Metric vs. Imperial

Two measurement systems dominate screw sizing: metric (mm) and imperial (inches).

  • Metric screws (e.g., M4, M5, M6) specify diameter, pitch, and length in millimeters.
    • M5×0.8×25 indicates 5mm diameter, 0.8mm thread spacing, 25mm length.
  • Imperial screws (e.g., #6, #8, 1/4″) combine diameter and threads per inch (TPI).
    • #10-24 means size #10 diameter with 24 threads per inch.

Most Common Screw Sizes & Their Uses

Wood Screws

Screw SizeCommon Lengths (in)Typical Use
#4½ to 1½Small trim, hinges
#6½ to 2Cabinet doors, light-duty wood joints
#8¾ to 3General woodworking, furniture
#101 to 4Framing, decking
#121½ to 5Structural woodwork, outdoor builds

Sheet Metal Screws

Screw SizeCommon Lengths (in)Typical Use
#6⅜ to 2Electrical boxes, light metal fixtures
#8½ to 3HVAC ducts, appliance repair
#10¾ to 3Car panels, garage doors

Machine Screws

Screw SizeThread SizeTypical Use
#4-40Fine threadElectronics, small devices
#6-32StandardComputer cases, light electrical
#8-32StandardSwitch plates, machine assembly
#10-24CoarseTool repair, machinery housing

Drywall Screws

SizeLength (in)Typical Use
#61 to 2¼” to ⅝” drywall to wood
#81¼ to 3Drywall to metal studs
Coarse Thread–Wood studs
Fine Thread–Metal studs

Concrete/Masonry Screws (e.g., Tapcon)

DiameterLength (in)Typical Use
3/16″1¼ to 3¼Hanging frames, light fixtures
¼”1¾ to 4Securing brackets, shelves to concrete

Lag Screws (Lag Bolts)

DiameterLength (in)Typical Use
¼” to ½”1½ to 6+Deck framing, heavy timber

Metric Machine Screws (Common in Europe/Asia)

SizeThread PitchTypical Use
M30.5 mmSmall electronics
M40.7 mmComputers, robotics
M50.8 mmAutomotive, bikes
M61.0 mmFurniture, large machines

How to Measure Screw Sizes Correctly

Three measurements define screw compatibility:

  1. Diameter – Calipers determine shaft thickness.
  2. Thread Pitch – Metric: distance between threads. Imperial: TPI count.
  3. Length – Head-to-tip for round heads; head-excluded for flat heads.

A #12-24×1.5″ screw has #12 diameter, 24 TPI, and 1.5-inch length.

Screw Size Charts for Quick Reference

A. Metric Screw Size Chart

Diameter (mm)Common Lengths (mm)Typical Use
M412–40Light fixtures
M620–80Furniture assembly
M1030–120Structural beams

B. Imperial Screw Size Chart

Diameter (inches)Threads Per Inch (TPI)Common Lengths (inches)
#8323/4″–3″
5/16″181″–4″
1/2″132″–8″

Choosing the Right Screw for Your Project

A. Material Compatibility

  • Softwoods – Coarse threads resist splitting.
  • Hard metals – Fine threads ensure tight seals.
  • Concrete – Masonry screws with carbide tips.

B. Weight Requirements

  • Under 10kg – M4/#8 screws suffice.
  • Over 100kg – M12/1/2″ screws with reinforcement plates.

C. Environmental Factors

  • Marine environments – 316-grade stainless steel resists saltwater corrosion.

FAQ

1. How does M5 compare to #10 screws?

  • M5 = 5mm diameter; #10 ≈ 4.8mm. Not directly interchangeable.

2. Can imperial screws fit metric nuts?

  • Thread angles differ—forced pairing damages components.

3. What screw size holds TV wall mounts?

  • M8 or 5/16″ screws with wall anchors support 50–100kg loads.

4. Why do some screws have twin threads?

  • Dual threads insert faster while maintaining grip strength.

5. How long should decking screws be?

  • 2.5 times the board thickness prevents surface splitting.

6. What distinguishes self-tapping screws?

  • Sharp tips cut threads into materials without pre-drilling.

7. When are washers necessary?

  • Soft materials like plastic require washers to distribute pressure.

8. Can screws replace nails in framing?

  • Structural screws meet code requirements; standard screws lack shear strength.

9. What causes screw heads to strip?

  • Incorrect driver bits or excessive torque deform head slots.

10. Where do screw size standards originate?

  • ISO governs metric sizes; ANSI regulates imperial measurements.

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