National Pipe Thread (NPT) Tap Drill Size

Below is the National Pipe Thread – NPT Tap Drill Size Chart.  It tells us what size hole must be drilled to begin tapping the tapered NPT thread.

Standard NPT Tap Drill Sizes

NPT Size
 Tap Drill Size (in.)
Decimal Equivalent (in.)
1/16 – 27
“C”
0.242
1/8 – 27
“Q”
0.332
1/4 – 18
7/16
0.438
3/8 – 18
9/16
0.562
1/2 – 14
45/64
0.703
3/4 – 14
29/32
0.906
1.0 – 11•1/2
1•9/64
1.141
1•1/4 – 11•1/2
1•31/64
1.484
1•1/2 – 11•1/2
1•23/32
1.719
2.0 – 11•1/2
2•3/16
2.188
2•1/2 – 8
2•39/64
2.609
3.0 – 8
3•15/64
3.234

Metric Tap Drill Sizes
Standard UNC Tap Drill Sizes
Standard UNF Tap Drill Sizes