VALICALC · TECHNICAL REFERENCE

Rectangular to Round Duct Chart

Compare rectangular duct area, hydraulic diameter and equal-area round diameter. Transfer actual rectangular dimensions to the existing Duct Size tool.

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SELECTED REFERENCE

400 × 200 mm

Equal-area round diameter
319.154 mm
Hydraulic diameter
266.667 mm
Cross-sectional area
80,000 mm²
All fields & cell provenance
Width
400 mm
Height
200 mm
Aspect ratio
2

v1.2.0 · verified 2026-10-06

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400 × 200 mm319.154 mmBack to answer ↑

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12 matching rows · 12 in this subset

Rectangular to Round Duct Chart, metric display
Rectangular exampleEqual-area round diameterHydraulic diameterCross-sectional areaActions
200 × 100 mm159.577 mm133.333 mm20,000 mm²
250 × 150 mm218.51 mm187.5 mm37,500 mm²
300 × 150 mm239.365 mm200 mm45,000 mm²
300 × 200 mm276.395 mm240 mm60,000 mm²
11.999999999999998 × 8 in280.818 mm243.84 mm61,935.36 mm²
400 × 200 mm319.154 mm266.667 mm80,000 mm²
16 × 8 in324.26 mm270.933 mm82,580.48 mm²
400 × 300 mm390.882 mm342.857 mm120,000 mm²
500 × 250 mm398.942 mm333.333 mm125,000 mm²
600 × 300 mm478.731 mm400 mm180,000 mm²
600 × 400 mm552.791 mm480 mm240,000 mm²
800 × 400 mm638.308 mm533.333 mm320,000 mm²

200 × 100 mm

Equal-area round diameter
159.577 mm
Hydraulic diameter
133.333 mm
Cross-sectional area
20,000 mm²
More dimensions
Width
200 mm
Height
100 mm
Aspect ratio
2

250 × 150 mm

Equal-area round diameter
218.51 mm
Hydraulic diameter
187.5 mm
Cross-sectional area
37,500 mm²
More dimensions
Width
250 mm
Height
150 mm
Aspect ratio
1.667

300 × 150 mm

Equal-area round diameter
239.365 mm
Hydraulic diameter
200 mm
Cross-sectional area
45,000 mm²
More dimensions
Width
300 mm
Height
150 mm
Aspect ratio
2

300 × 200 mm

Equal-area round diameter
276.395 mm
Hydraulic diameter
240 mm
Cross-sectional area
60,000 mm²
More dimensions
Width
300 mm
Height
200 mm
Aspect ratio
1.5

11.999999999999998 × 8 in

Equal-area round diameter
280.818 mm
Hydraulic diameter
243.84 mm
Cross-sectional area
61,935.36 mm²
More dimensions
Width
304.8 mm
Height
203.2 mm
Aspect ratio
1.5

400 × 200 mm

Equal-area round diameter
319.154 mm
Hydraulic diameter
266.667 mm
Cross-sectional area
80,000 mm²
More dimensions
Width
400 mm
Height
200 mm
Aspect ratio
2

16 × 8 in

Equal-area round diameter
324.26 mm
Hydraulic diameter
270.933 mm
Cross-sectional area
82,580.48 mm²
More dimensions
Width
406.4 mm
Height
203.2 mm
Aspect ratio
2

400 × 300 mm

Equal-area round diameter
390.882 mm
Hydraulic diameter
342.857 mm
Cross-sectional area
120,000 mm²
More dimensions
Width
400 mm
Height
300 mm
Aspect ratio
1.333

500 × 250 mm

Equal-area round diameter
398.942 mm
Hydraulic diameter
333.333 mm
Cross-sectional area
125,000 mm²
More dimensions
Width
500 mm
Height
250 mm
Aspect ratio
2

600 × 300 mm

Equal-area round diameter
478.731 mm
Hydraulic diameter
400 mm
Cross-sectional area
180,000 mm²
More dimensions
Width
600 mm
Height
300 mm
Aspect ratio
2

600 × 400 mm

Equal-area round diameter
552.791 mm
Hydraulic diameter
480 mm
Cross-sectional area
240,000 mm²
More dimensions
Width
600 mm
Height
400 mm
Aspect ratio
1.5

800 × 400 mm

Equal-area round diameter
638.308 mm
Hydraulic diameter
533.333 mm
Cross-sectional area
320,000 mm²
More dimensions
Width
800 mm
Height
400 mm
Aspect ratio
2

How to use this data

A=ab; Dequal-area=√(4ab/π); Dhydraulic=4A/P=2ab/(a+b). Send the original rectangle dimensions into Duct Size for its documented approximate loss method.

    CHECK THE METHOD

    Worked example

    400×200 mm gives area 80000 mm², hydraulic diameter 266.667 mm and equal-area round diameter about 319.154 mm.

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    ReferenceRound Duct CFM ChartReferenceDuct Velocity Reference

    Common lookup questions

    Can I use these values as a universal specification?

    Equal area does not mean equal friction, noise or fan duty. A round replacement requires a separately verified airflow/resistance model.

    TRACEABLE DATA

    Sources, scope & verification

    Dataset v1.2.0
    Last verified:

    12 authored geometry examples. Equal area and hydraulic diameter are two different quantities; no equal-friction conversion is claimed.

    Values are curated product facts or generated scenarios. Paid standards, complete catalogs and source diagrams are not reproduced. A verification date applies to this documented subset.

    Duct area and airflow relationship ↗

    Type A · Greenheck · Options, Accessories and Engineering, October 2021, ACC-34

    Original generated scenarios from the stated equations; source tables/text/drawings are not reproduced.

    Full provenance & artifact record
    Source checked
    2026-10-06
    Use basis
    authored-formula
    Artifact SHA-256
    No retained source artifact hash; see the stated source and verification record.