Where does the 0.40849 constant come from?

A US gallon is 231 in³, a minute is 60 s and a foot is 12 in. The constant is 231 ÷ 60 ÷ 12 ÷ (π ÷ 4), which turns gal/min and in² into ft/sec. It is not user data.

What velocity limit should I use?

Common plant practice caps discharge lines near 10 ft/sec and suction lines near 5 ft/sec to limit erosion and noise. Your piping standard or pump vendor may set tighter limits.

Why does the area row not need a schedule table?

The area falls out of the inside diameter: π × d² ÷ 4. Enter the inside diameter from the schedule, and the area row follows without a separate lookup.

Why did the old conversion factor input disappear?

0.321 was a unit conversion, not plant data. V2 folds it into the 0.40849 constant, so the only entries are flow, inside diameter and the limit.

Process Manufacturing calculator

Pipe Velocity Calculator

Find the velocity a flow produces in a pipe, or the flow a velocity limit allows. You need the volumetric flow, the pipe inside diameter and the maximum velocity.

What this calculator does

Fluid velocity in a pipe from flow and inside diameter, against a maximum velocity limit.

Formula used

Velocity (ft/sec) = 0.40849 × flow (gal/min) ÷ inside diameter² (in²)
Inside flow area = π × diameter² ÷ 4
Velocity (m/sec) = velocity (ft/sec) × 0.3048
Flow at velocity limit = limit × diameter² ÷ 0.40849; headroom = limit − velocity

Inputs explained

Process Flow: Volumetric flow through the pipe at line temperature.
Pipe Inside Diameter: Inside diameter from the pipe schedule or vendor table.
Maximum Velocity: Velocity limit your standard or vendor sets for this line.

How to use the result

Best suited to sizing a line for a target velocity, checking a suction line against a low limit, finding the flow a velocity limit allows.
Velocity varies across the pipe; this is the bulk average. Corrosion, erosion and noise limits differ by service; use the limit your standard sets.

Current U.S. benchmarks

The producer price index for industrial chemicals stands at 336.006 (BLS, Aug 2026), up 13.3% from a year earlier. Quotes priced off last quarter's material cost miss this move.
The U.S. has 14,543 chemical manufacturing establishments employing about 911,245 workers (Census County Business Patterns, 2023).

Common questions

Where does the 0.40849 constant come from? A US gallon is 231 in³, a minute is 60 s and a foot is 12 in. The constant is 231 ÷ 60 ÷ 12 ÷ (π ÷ 4), which turns gal/min and in² into ft/sec. It is not user data.
What velocity limit should I use? Common plant practice caps discharge lines near 10 ft/sec and suction lines near 5 ft/sec to limit erosion and noise. Your piping standard or pump vendor may set tighter limits.
Why does the area row not need a schedule table? The area falls out of the inside diameter: π × d² ÷ 4. Enter the inside diameter from the schedule, and the area row follows without a separate lookup.
Why did the old conversion factor input disappear? 0.321 was a unit conversion, not plant data. V2 folds it into the 0.40849 constant, so the only entries are flow, inside diameter and the limit.

Last reviewed 2026-10-01.