ACCA Duct Calculator
Calculate Manual D-style available static pressure, total effective length, design friction rate and preliminary round-duct diameter from airflow and velocity. Enter your own values and review every assumption shown with the result.
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The primary result is displayed first, followed by supporting values that make the estimate easier to verify.
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How to Use This Calculator
Enter each requested value using the displayed unit. Replace the example defaults with source-specific values and review all assumptions.
Formula & Methodology
The calculator applies the displayed formulas directly to the entered values. Supporting outputs expose important intermediate calculations.
Worked example
With 0.50 in. w.c. external static pressure, 0.25 in. w.c. component losses and 200 ft total effective length, the design friction rate is 0.125 in. w.c. per 100 ft.
The diameter output is only a velocity-based preliminary size, not a full Manual D duct selection. Proper design requires blower data, pressure losses, fitting equivalent lengths, duct material, friction charts, branch airflow, balancing and verified system operating point.
This tool is not ACCA-approved software and is not a replacement for ANSI/ACCA Manual D, manufacturer data or qualified HVAC design. ACCA is a trademark of its owner.
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Related Guides
- How Manual D Friction Rate and Duct Sizing WorksUnderstand how ACCA Manual D duct design works — how available static pressure and friction rate determine duct sizes, and how to calculate CFM requirements for each room.
- Duct CFM Calculator: How to Size HVAC Ductwork for Proper AirflowUnderstand how to calculate CFM requirements for HVAC ductwork using room size, air changes per hour, and the Manual D friction rate method.
- How to Calculate the Right Fuse Size for Electrical CircuitsLearn how to determine the correct fuse or circuit breaker size for any electrical circuit — based on load current, conductor size, NEC overcurrent protection rules, and motor starting current.
- How Three-Phase Motor Amperage Is Calculated from HP and VoltageLearn the three-phase motor current formula — how to calculate full-load amps from horsepower, voltage, motor efficiency, and power factor, with NEC table values for quick reference.
- How to Convert Amp Hours to Watt HoursLearn how to use the Amp Hour to Watt Hour Calculator, understand its formula and interpret the result.
Frequently Asked Questions
- What does the ACCA Duct Calculator calculate?
- Calculate Manual D-style available static pressure, total effective length, design friction rate and preliminary round-duct diameter from airflow and velocity.
- Can I change the assumptions?
- Yes. Replace the example defaults with values from the current game, project, product, drawing, data sheet or market source.
- Is the result exact?
- No. It is an estimate produced by the displayed formulas and entered assumptions. Real results may differ because of factors described in the limitations section.
- Should an important result be verified?
- Yes. Verify important decisions with current source data, official documentation, manufacturer information or a qualified professional.
Last updated 7/22/2026