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NPT Pipe Thread Dimension Calculator — ASME B1.20.1 Thread Data

Look Up NPT, NPTF, and BSPT Thread Dimensions with Tap Drill Sizes

Free pipe thread calculator covering 14 pipe sizes (1/8" through 8") in three standards: NPT, NPTF, and BSPT. All dimensions per ASME B1.20.1 and BS EN 10226-1. See pitch, thread height, major/pitch/minor diameter, taper rate, and tap drill size.

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Includes thread engagement diagram and standard comparison panel explaining NPT vs NPTF vs BSPT differences. Tap drill lookup references 190+ standard drill sizes.

Pro Tip: NPT requires pipe dope or Teflon tape to seal. NPTF (dryseal) creates a metal-to-metal seal without sealant when tightened properly. Know which standard the mating fitting uses before you start cutting threads — using an NPT tap where NPTF is expected will leak without sealant.

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Pipe Thread Dimension Calculator
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How It Works

  1. Select Pipe Size

    Choose nominal size from 1/8" through 8". Remember: pipe sizes are nominal, not actual OD.

  2. Select Standard

    Choose NPT, NPTF (dryseal), or BSPT. Each has slightly different thread geometry.

  3. Review Dimensions

    See TPI, pitch, thread height, major/pitch/minor diameters, taper rate, and engagement length in inches and mm.

  4. Get Tap Drill Size

    Calculator shows recommended tap drill and nearest standard drill size.

  5. Compare Standards

    Comparison panel explains practical differences in sealing, interchangeability, and applications.

Built For

  • Plumbers and pipefitters verifying thread dimensions for code-compliant installations
  • Machinists setting up lathes to cut NPT or BSPT pipe threads
  • Hydraulic technicians selecting correct thread standards for pressure connections
  • Maintenance mechanics identifying pipe threads for replacement parts
  • CNC programmers setting up pipe thread cycles
  • Students learning NPT, NPTF, and BSPT standards

Features & Capabilities

14 Pipe Sizes

1/8" through 8" nominal sizes with complete dimension data.

Three Standards

NPT (ASME B1.20.1), NPTF (ASME B1.20.3), BSPT (BS EN 10226-1).

Thread Engagement Diagram

Visual representation of tapered thread mating geometry.

Standard Comparison

Side-by-side explanation of sealing methods and interchangeability.

190+ Drill Lookup

Automatic tap drill selection from standard drill database.

PDF Export

Export thread data as branded PDF for lathe reference.

Frequently Asked Questions

They screw together (same pitch, diameter, taper) but NPT requires sealant while NPTF is designed for metal-to-metal seal without sealant.
3/4 inch per foot (1 in 16), which equals 1 degree 47 minutes per side. Same taper rate for NPT, NPTF, and BSPT.
With sealant: 3-5 turns past hand tight. For NPTF dryseal: 2-3 turns past hand tight. Over-tightening can crack female fittings, especially cast iron and brass.
Pipe tap drills are sized for the minor diameter at the small end of the taper. The tap cuts progressively deeper as it advances into the tapered hole.
Disclaimer: Dimensions per ASME B1.20.1, ASME B1.20.3, and BS EN 10226-1. For pressure-rated connections, verify threads with calibrated pipe thread gauges (L1, L2).

Learn More

Machinist

NPT vs NPTF vs BSP — Pipe Thread Standards Compared

Differences between NPT, NPTF, BSPT, and BSPP pipe threads. Thread geometry, sealing mechanisms, when to use each, and why they don't interchange.

Read Guide →

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