What is the relationship between flow, velocity and diameter?

Use Q = v · A and A = πD²/4. With those equations you can solve for the unknown you need in each segment.

Why does velocity matter in a pipe?

Velocity affects head losses, noise, erosion and cavitation risk. Sizing with limits avoids problematic designs.

How do I choose the recommended commercial diameter?

The calculator takes the list of commercial diameters and chooses the smallest that satisfies the velocity limits or the closest to the target within the range.

What does “series” mean in multiple segments?

In series, the flow is the same in all segments. Each diameter produces a different velocity but Q remains constant.

How are volume and travel time interpreted?

Volume is V = A · L and travel time is t = L / v. They are useful for estimating filling or emptying times per segment.

Does it have regulatory limitations?

It is a reference calculator. For regulated projects you should check local standards and specific design criteria.

What units can I use?

You can work with m³/s, m³/h, L/s or L/min for flow and mm/in for diameter. The calculator converts everything internally to SI.

Can two different scenarios be compared?

Yes. Compare mode lets you define scenarios A/B with their segments, constraints and a summary of velocities, volume and time.

Flow, velocity and diameter calculator for pipes

Calculate flow, velocity or diameter across multiple segments, size with velocity limits, compare A/B scenarios, visualize SVG, export CSV and generate a printable report.

Flow / Velocity / Diameter (multi-segment sizing)

Solve Q–v–D per segment, size with velocity limits, compare scenarios and generate reports with SVG visualization.

Input data

I want to calculate

Flow (Q)

Velocity (v) m/s

Diameter (D)

Basic

Series (same Q in all segments)

Advanced

Show L, V and t columns Length L is optional and enables volume and travel time.

Segments

Label	Int. D	Segment Q	L	Actions

Results

CSV separator

Global Q —

v min —

v max —

Fastest —

Slowest —

Recommended D —

Commercial D —

Segment	D	A	Q	v	L	V	t	Status

Segment visualization

Sizing

Global flow (Q)

Velocity constraint

v max (m/s)

v min (m/s)

v target (m/s)

Commercial diameters (mm)

Apply to

Segment to size

Sizing result

Recommended D —

Commercial D —

Resulting v —

Segment	Recommended D	Commercial D	v	Status

Sized segment view

Compare scenarios A/B

Scenario A

Flow (Q)

v max (m/s)

Commercial diameters (mm)

Segments

Label	Int. D	L	Actions

SVG A

Scenario B

Flow (Q)

v max (m/s)

Commercial diameters (mm)

Segments

Label	Int. D	L	Actions

SVG B

Comparative summary

Commercial D A —

Commercial D B —

v max A —

v max B —

Total volume A —

Total volume B —

Total time A —

Total time B —

Input data

Segments

Results

Segment visualization

Sizing

Sizing result

Sized segment view

Compare scenarios A/B

Scenario A

Segments

SVG A

Scenario B

Segments

SVG B

Comparative summary

Step by step per segment

You may also like

Pipe head loss calculator (Darcy–Weisbach)

Fluid mixing: final temperature, concentration & density

Open channel flow (Manning): normal & critical depth