PEX Pipe Sizing Calculator & Complete Guide
Calculate PEX pipe sizing, flow rates, and capacity. Complete guide to PEX pipe properties, C-values, applications, and installation with free calculator.
PEX (cross-linked polyethylene) pipe has revolutionized residential plumbing with its flexibility, ease of installation, and cost-effectiveness. Since its introduction in the 1980s, PEX has become the preferred choice for many plumbers and homeowners. This comprehensive guide covers PEX pipe sizing, flow characteristics, installation methods, and best practices for designing efficient PEX plumbing systems.
Key Characteristics
Friction Characteristics
PEX pipe has a Hazen-Williams C-value of 150, making it smoother than copper (C=140) and allowing for slightly better flow capacity. The smooth interior surface and flexibility reduce installation friction and maintain consistent flow rates throughout the system.
Temperature Resistance
PEX pipe is rated for continuous operation at 180°F and can handle temperatures up to 200°F for short periods. PEX-A (most flexible) has the best temperature resistance, while PEX-B and PEX-C have similar but slightly lower ratings. PEX is excellent for both hot and cold water applications.
Flexibility & Installation
PEX's flexibility allows for fewer fittings, reducing potential leak points and installation time. It can bend around corners without elbows, reducing friction loss from fittings. PEX is also freeze-resistant - it can expand up to 3 times its diameter without bursting, then return to normal size.
Pressure Ratings
Standard PEX pipe is rated for 160 PSI at 73°F and 100 PSI at 180°F. These ratings are suitable for all residential and most commercial applications. PEX maintains its pressure rating better than copper at higher temperatures.
PEX Pipe Flow Capacity (C=150)
Maximum recommended flow rates (GPM) for standard PEX pipe at velocity of 6 ft/s. PEX's higher C-value (150) provides slightly better flow than copper for the same diameter.
| Nominal Size | Inside Diameter (in) | OD (in) | Max Flow @ 6 ft/s (GPM) | Pressure @ 73°F (PSI) |
|---|---|---|---|---|
| 1/2" | 0.485 | 0.625 | 3.3 | 160 |
| 3/4" | 0.700 | 0.875 | 6.9 | 160 |
| 1" | 0.945 | 1.125 | 12.6 | 160 |
| 1-1/4" | 1.245 | 1.375 | 21.9 | 160 |
| 1-1/2" | 1.480 | 1.625 | 31.0 | 160 |
| 2" | 1.935 | 2.125 | 54.1 | 160 |
| 3" | 2.900 | 3.125 | 121.5 | 160 |
Advantages
- Excellent flexibility - fewer fittings needed
- Freeze-resistant (expands without bursting)
- Smooth interior (C=150) for efficient flow
- Lower cost than copper
- Faster installation (crimp or expansion fittings)
- No corrosion concerns
- Quieter operation (reduces water hammer)
- Long lifespan (50+ years expected)
Disadvantages
- Not suitable for outdoor exposure (UV degradation)
- Cannot be used for direct burial without protection
- Requires special tools for installation
- Not recyclable like copper
- May have slight plastic taste initially
- Some codes restrict PEX in certain applications
- Requires proper support (sags more than rigid pipe)
Frequently Asked Questions
Code Compliance
PEX is approved by IPC, UPC, and most local codes for water supply applications. Some jurisdictions may restrict PEX for certain applications (e.g., direct burial, outdoor exposure). Always verify local code requirements before installation.