Why scale from a measured point instead of a resistance factor?

A measured point already contains the line's length, diameter, fittings, filter and fluid. Squaring the flow ratio then moves the drop to the new flow without four numbers you cannot audit.

What if the line runs laminar rather than turbulent?

The square law assumes turbulent flow. In laminar flow the drop rises nearly with flow itself, so this estimate is an upper bound there. Check the Reynolds number when in doubt.

How do I pick the allowable pressure drop?

Take the lowest of the pump's spare head, the control valve's authority and the equipment's maximum. The default 15 psi suits a short wash or transfer line.

Does elevation between the gauge points show up here?

No. The measured reference drop is friction only if both gauges sit at the same elevation. Add static head separately, about 0.433 psi per foot of rise for water.

Process Manufacturing calculator

Pressure Drop Calculator

Scale a line's pressure drop from a measured operating point to a new flow with the square law, then check it against your allowable. You need the reference flow and drop, the design flow, the specific gravity and the allowable.

What this calculator does

Pressure drop for a design flow scaled from one measured reference point, and whether it fits the allowable.

Formula used

Estimated drop = reference drop × (design flow ÷ reference flow)² × specific gravity
Allowable margin = allowable drop − estimated drop
Flow at allowable = reference flow × √(allowable ÷ (reference drop × specific gravity))
Drop share of allowable = estimated drop ÷ allowable × 100

Inputs explained

Reference Flow: Flow at the measured operating point; the same line and fluid.
Measured Drop at Reference: Gauge difference across the line at the reference flow.
Design Flow: Flow the line must pass in the new operating case.
Fluid Specific Gravity: Fluid specific gravity relative to water at line temperature.
Allowable Pressure Drop: Most drop the line may take at the design flow.

How to use the result

Best suited to scaling a wash line to a higher flow, checking a brine line at higher specific gravity, finding the flow that fits an allowable drop.
Static elevation head is excluded; add it separately if the line changes height. Laminar lines scale closer to linearly, so the square law overstates them at low flow.

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

Why scale from a measured point instead of a resistance factor? A measured point already contains the line's length, diameter, fittings, filter and fluid. Squaring the flow ratio then moves the drop to the new flow without four numbers you cannot audit.
What if the line runs laminar rather than turbulent? The square law assumes turbulent flow. In laminar flow the drop rises nearly with flow itself, so this estimate is an upper bound there. Check the Reynolds number when in doubt.
How do I pick the allowable pressure drop? Take the lowest of the pump's spare head, the control valve's authority and the equipment's maximum. The default 15 psi suits a short wash or transfer line.
Does elevation between the gauge points show up here? No. The measured reference drop is friction only if both gauges sit at the same elevation. Add static head separately, about 0.433 psi per foot of rise for water.

Last reviewed 2026-10-01.