Schedule 40 PVC friction loss chart
Each value is the pressure lost to friction, in psi, for every 100 ft of pipe at that flow. Cells marked * and shaded have a water velocity above 5 ft/s, the usual upper limit for irrigation pipe. Hover over a value on a computer to see its velocity.
| Flow | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" | 2-1/2" | 3" | 4" |
|---|---|---|---|---|---|---|---|---|---|
| 1 GPM | 0.50 | 0.12 | 0.04 | 0.01 | — | — | — | — | — |
| 2 GPM | 1.82 | 0.44 | 0.13 | 0.03 | 0.02 | — | — | — | — |
| 5 GPM | 9.92* | 2.43 | 0.73 | 0.19 | 0.09 | 0.03 | — | — | — |
| 7 GPM | 18.49* | 4.53 | 1.36 | 0.35 | 0.16 | 0.05 | 0.02 | — | — |
| 10 GPM | 35.80* | 8.76* | 2.64 | 0.68 | 0.32 | 0.09 | 0.04 | 0.01 | — |
| 15 GPM | — | 18.56* | 5.59* | 1.44 | 0.67 | 0.20 | 0.08 | 0.03 | — |
| 20 GPM | — | 31.63* | 9.52* | 2.45 | 1.15 | 0.34 | 0.14 | 0.05 | 0.01 |
| 25 GPM | — | — | 14.39* | 3.71* | 1.73 | 0.51 | 0.21 | 0.07 | 0.02 |
| 30 GPM | — | — | 20.17* | 5.19* | 2.43 | 0.71 | 0.30 | 0.10 | 0.03 |
| 35 GPM | — | — | — | 6.91* | 3.23* | 0.94 | 0.40 | 0.14 | 0.04 |
| 40 GPM | — | — | — | 8.85* | 4.14* | 1.21 | 0.51 | 0.18 | 0.05 |
| 45 GPM | — | — | — | 11.00* | 5.15* | 1.51 | 0.63 | 0.22 | 0.06 |
| 50 GPM | — | — | — | 13.38* | 6.25* | 1.83 | 0.77 | 0.27 | 0.07 |
| 60 GPM | — | — | — | — | 8.77* | 2.56* | 1.08 | 0.37 | 0.10 |
| 70 GPM | — | — | — | — | — | 3.41* | 1.44 | 0.50 | 0.13 |
| 75 GPM | — | — | — | — | — | 3.88* | 1.63* | 0.56 | 0.15 |
| 80 GPM | — | — | — | — | — | 4.37* | 1.84* | 0.64 | 0.17 |
| 90 GPM | — | — | — | — | — | 5.43* | 2.29* | 0.79 | 0.21 |
| 100 GPM | — | — | — | — | — | 6.60* | 2.78* | 0.96 | 0.25 |
| 125 GPM | — | — | — | — | — | 9.98* | 4.21* | 1.45* | 0.38 |
| 150 GPM | — | — | — | — | — | — | 5.90* | 2.04* | 0.54 |
Class 200 (SDR 21) PVC friction loss chart
Class 200 PVC has a thinner wall than Schedule 40, so each nominal size has a larger inside diameter and lower friction loss at the same flow. It's widely used for irrigation mainlines and laterals.
| Flow | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" | 2-1/2" | 3" | 4" |
|---|---|---|---|---|---|---|---|---|
| 1 GPM | 0.07 | 0.02 | 0.01 | 0.00 | — | — | — | — |
| 2 GPM | 0.24 | 0.07 | 0.02 | 0.01 | 0.00 | — | — | — |
| 5 GPM | 1.33 | 0.39 | 0.12 | 0.06 | 0.02 | 0.01 | 0.00 | — |
| 7 GPM | 2.48 | 0.73 | 0.23 | 0.12 | 0.04 | 0.02 | 0.01 | — |
| 10 GPM | 4.80 | 1.42 | 0.45 | 0.23 | 0.08 | 0.03 | 0.01 | — |
| 15 GPM | 10.16* | 3.00 | 0.95 | 0.49 | 0.16 | 0.06 | 0.02 | — |
| 20 GPM | 17.31* | 5.12* | 1.61 | 0.83 | 0.28 | 0.11 | 0.04 | 0.01 |
| 25 GPM | — | 7.74* | 2.44 | 1.25 | 0.42 | 0.16 | 0.06 | 0.02 |
| 30 GPM | — | 10.85* | 3.42* | 1.75 | 0.59 | 0.23 | 0.09 | 0.03 |
| 35 GPM | — | 14.43* | 4.55* | 2.33 | 0.78 | 0.31 | 0.12 | 0.03 |
| 40 GPM | — | — | 5.83* | 2.99* | 1.00 | 0.39 | 0.15 | 0.04 |
| 45 GPM | — | — | 7.25* | 3.72* | 1.24 | 0.49 | 0.19 | 0.05 |
| 50 GPM | — | — | 8.81* | 4.52* | 1.51 | 0.59 | 0.23 | 0.07 |
| 60 GPM | — | — | — | 6.33* | 2.12* | 0.83 | 0.32 | 0.09 |
| 70 GPM | — | — | — | 8.42* | 2.82* | 1.10 | 0.42 | 0.12 |
| 75 GPM | — | — | — | 9.57* | 3.20* | 1.25 | 0.48 | 0.14 |
| 80 GPM | — | — | — | — | 3.61* | 1.41 | 0.54 | 0.16 |
| 90 GPM | — | — | — | — | 4.49* | 1.76* | 0.67 | 0.20 |
| 100 GPM | — | — | — | — | 5.46* | 2.14* | 0.82 | 0.24 |
| 125 GPM | — | — | — | — | — | 3.23* | 1.23* | 0.36 |
| 150 GPM | — | — | — | — | — | 4.53* | 1.73* | 0.51 |
Maximum flow for each pipe size at 5 ft/s
Velocity rises in direct proportion to flow, so the flow at 5 ft/s can be read straight from the velocity data behind the charts above. Staying at or below these flows is the first check when sizing pipe.
| Nominal size | Schedule 40 (GPM) | Class 200 / SDR 21 (GPM) |
|---|---|---|
| 1/2" | 4 | — |
| 3/4" | 7 | 10 |
| 1" | 12 | 16 |
| 1-1/4" | 22 | 26 |
| 1-1/2" | 30 | 35 |
| 2" | 51 | 55 |
| 2-1/2" | 73 | 81 |
| 3" | 113 | 121 |
| 4" | 195 | 200 |
Class 200 isn't made in 1/2-inch, so that cell is blank. For a flow and pipe not listed, the pipe velocity calculator works it out.
How to use the friction loss chart
- Find the flow the pipe section carries, in GPM. For a sprinkler lateral, that's the total flow of every head downstream of the section.
- Read the loss in the column for your pipe type and size.
- Add fittings as equivalent lengths of straight pipe (see fitting losses).
- Multiply the loss per 100 ft by the total length divided by 100.
Worked example
A 150 ft run of 1-inch Schedule 40 PVC carries 10 GPM and has two 90° elbows.
- Chart value: 2.64 psi per 100 ft, at 3.86 ft/s, under the 5 ft/s limit.
- Fittings: two 1-inch 90° elbows at 2.5 ft each add 5 ft, for 155 ft in total.
- Total loss: 2.64 × 155 ÷ 100 = 4.1 psi.
In 1-inch Class 200 pipe, the same run would lose about 1.42 × 1.55 = 2.2 psi. The irrigation pipe size calculator and mainline size calculator do this for any flow and length.
To convert: feet of head = psi ÷ 0.4332. For metric, 1 psi per 100 ft ≈ 22.6 kPa per 100 m.
Friction loss through PVC fittings
Fittings are counted as an equivalent length of straight pipe of the same size. Add them to the pipe length before applying the chart.
| Fitting | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" | 2-1/2" | 3" | 4" |
|---|---|---|---|---|---|---|---|---|---|
| Tee, flow through run | 1.0 | 1.4 | 1.7 | 2.3 | 2.7 | 4.0 | 4.9 | 6.1 | 7.9 |
| Tee, flow through branch | 3.8 | 4.9 | 6.0 | 7.3 | 8.4 | 12.0 | 14.7 | 16.4 | 22.0 |
| 90° elbow | 1.5 | 2.0 | 2.5 | 3.8 | 4.0 | 5.7 | 6.9 | 7.9 | 11.4 |
| 45° elbow | 0.8 | 1.1 | 1.4 | 1.8 | 2.1 | 2.6 | 3.1 | 4.0 | 5.1 |
Valves, backflow preventers and meters lose far more than fittings and are rated separately. See the valve pressure loss calculator and the backflow preventer pressure loss calculator.
The Hazen-Williams formula behind the chart
The chart values come from the Hazen-Williams equation, which Spears Manufacturing notes is widely used for water in PVC and CPVC pipe:
Friction head loss
f = 0.2083 × (100 ÷ C)^1.852 × G^1.852 ÷ d^4.8655
f = friction head in feet of water per 100 ft; C = roughness constant (150 for PVC); G = flow in US gallons per minute; d = inside diameter in inches. Divide feet of head by 2.31 (multiply by 0.4332) for psi.
Velocity
V = 0.3208 × G ÷ A
V = velocity in ft/s; A = inside cross-sectional area in square inches.
Because the loss depends on the inside diameter raised to nearly the fifth power, a small change in diameter has a big effect. That's why Schedule 40 and Class 200 pipe of the same nominal size give such different results, and why charts based on slightly different diameters can disagree by a few percent. Spears' values use the average inside diameter from mean wall thickness; actual pipe can vary.
Before you size pipe from the chart
- Keep velocity at or below 5 ft/s. The USDA NRCS irrigation pipeline standard says not to exceed 5 ft/s at design capacity. Faster water raises the risk of water hammer: Spears' surge chart shows that stopping water flowing at 5 ft/s instantly in 1-inch Schedule 40 PVC can produce a surge of about 119 psi.
- Count the whole path. Friction in pipe is only one loss. Add fittings, valves, backflow preventer, meter and elevation to see how much pressure reaches the sprinklers.
- Mind the pressure rating. The NRCS standard also advises keeping PVC working pressure at or below 72% of the pipe's temperature-adjusted pressure rating, as a safety factor against surges.
- Size laterals section by section. Flow drops after each sprinkler, so the pipe can often step down in size toward the end of a lateral. The sprinkler pipe size calculator handles this.
Frequently asked questions
How much pressure is lost in 100 feet of PVC pipe?
It depends on the pipe size and the flow. For Schedule 40 PVC at 10 GPM, Spears Manufacturing's tables give 8.76 psi per 100 ft for 3/4-inch pipe, 2.64 psi for 1-inch pipe and 0.68 psi for 1-1/4-inch pipe. Friction loss rises steeply with flow, so doubling the flow in the same pipe roughly triples to quadruples the loss.
What size PVC pipe do I need for my flow?
A common rule is to keep water velocity at or below 5 feet per second. Working from Spears Manufacturing's velocity data, that limits Schedule 40 PVC to about 7 GPM in 3/4-inch pipe, 12 GPM in 1-inch, 22 GPM in 1-1/4-inch and 30 GPM in 1-1/2-inch pipe. Then check that the total friction loss over the pipe's length still leaves enough pressure for your sprinklers.
Why should water velocity in PVC pipe stay under 5 feet per second?
Faster water causes bigger pressure surges, called water hammer, when a valve closes or a pump stops. The USDA NRCS irrigation pipeline standard says not to exceed 5 feet per second at design capacity, and Spears Manufacturing recommends the same limit for plastic piping systems to minimize hydraulic shock.
Does Class 200 PVC have less friction loss than Schedule 40?
Yes, in the same nominal size. Class 200 (SDR 21) pipe has a thinner wall, so its inside diameter is larger and water flows more easily. At 10 GPM, Spears lists 1.42 psi per 100 ft for 1-inch SDR 21 against 2.64 psi for 1-inch Schedule 40.
What C value is used for PVC pipe in the Hazen-Williams formula?
A C value of 150 is the commonly accepted value for PVC and CPVC pipe, according to Spears Manufacturing. Higher C values mean smoother pipe and lower friction loss. All the values on this page use C = 150.
Do fittings add friction loss?
Yes. Each fitting adds loss, usually expressed as an equivalent length of straight pipe. Spears lists about 2.5 ft for a 1-inch 90-degree elbow and 6.0 ft for flow through the branch of a 1-inch tee. Add these equivalent lengths to the pipe length before calculating the total loss.
Who built and checked this chart
Licensed Professional Engineer and Irrigation Association Certified Irrigation Designer with more than 20 years in irrigation design, system auditing and landscape water management. Full profile
How this page was checked
- Every friction and velocity value transcribed from Spears' published tables and checked row by row.
- Maximum flows at 5 ft/s recalculated from the tabulated velocities.
- Worked example recalculated by hand from the chart and fitting values.
Sources
- Spears Manufacturing Company. Engineering & Design Data: Flow Velocity & Friction Loss, Hydraulic Shock. Schedule 40 and SDR 21 friction loss tables, fitting losses and surge pressures.
- USDA Natural Resources Conservation Service. Conservation Practice Standard: Irrigation Pipeline (Code 430).