Dryer-Ell Measures the Sames as Straight Pipe
Unlike sectioned elbows, the Dryer-Ell allows use of the full code-allowable length of run. Generally, building code requires a reduction in duct length for all other dryer elbows.
The Dryer-Ell is engineered for a one-to-one ratio with standard straight pipe.

With two sectioned elbows instead of the Dryer-Ells shown, this run would have been counted about ten feet longer than its actual length.The Dryer-Ell was specifically designed to minimize airflow friction loss. You may learn more about the design methodology under the ASHRAE Calculations subsection of Product Detail / White Papers.
Current building code from the International Code Council now also includes tables (IMC 504.6.4.1 and IRC M1502.4.4.1) that delineate an equivalent length for the Dryer-Ell that is the same as its actual length.
The bottom line: Dryer-Ells measure a one to one ratio with straight pipe.
The Dryer-Ell is engineered for a one-to-one ratio with standard straight pipe.

With two sectioned elbows instead of the Dryer-Ells shown, this run would have been counted about ten feet longer than its actual length.
Current building code from the International Code Council now also includes tables (IMC 504.6.4.1 and IRC M1502.4.4.1) that delineate an equivalent length for the Dryer-Ell that is the same as its actual length.
The bottom line: Dryer-Ells measure a one to one ratio with straight pipe.
Measures
Same as Straight Pipe
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Same as Straight Pipe
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Airflow Efficient Elbows
New tables in 2009 IMC and IRC show an equivalent length for 10" radius smooth elbows that match the Dryer-Ell's actual length.
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Ten Inch Radius Smooth Dryer Duct Elbows
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