An online ductulator is a digital version of the slide-rule wheel techs have carried for decades. Whether you search for duct u lator, ductulator calculator, or mcquay duct sizer, you are looking for the same thing: given a CFM requirement and a friction rate, what duct diameter (round or rectangular) keeps airflow quiet and the blower within its static pressure budget.
What a Ductulator Does
A ductulator balances two limits:
- Friction rate — static pressure lost per 100 ft of duct (typically 0.08–0.10 in.wg/100 ft residential)
- Velocity — air speed in fpm (keep branch runs under ~900 fpm, trunks under ~700 fpm for quiet operation)
Input CFM and friction rate → output duct size. Input duct size and CFM → output friction rate. That bidirectional lookup is what separates a duct sizer from a simple CFM chart.
How a ductulator resolves inputs to outputs
Online Ductulator vs Physical Wheel
| Tool | Pros | Cons |
|---|---|---|
| Physical ductulator | Fast in the field, no battery | One friction rate at a time |
| Online ductulator | Rectangular equivalents, save runs | Needs phone or laptop |
| Mcquay duct sizer | Industry-standard desktop app | Paid license for full features |
| Spreadsheet | Custom friction tables | Error-prone without validation |
Our HVAC Duct Size Calculator works as a duct calculator online for round and rectangular sizing at your chosen friction rate.
Duct sizing tool comparison
How to Use a Ductulator Step by Step
- Know your CFM — from equipment specs or a room/airflow calc
- Pick friction rate — 0.10 in.wg/100 ft is the residential default; Manual D refines this from blower capacity
- Look up round size — e.g. 400 CFM → ~10 in round at 0.10
- Check velocity — if above target, go one size larger
- Convert to rectangular if needed — equal cross-sectional area (see Duct Size Chart)
Round duct size by airflow at 0.10 in.wg/100 ft
When You Need More Than a Ductulator
A ductulator calculator sizes one duct segment. Manual D sizes the whole system: trunk, branches, fittings, and total external static pressure. For whole-system design, start with HVAC Duct Sizing Guide.
Flex duct carries 15–20% less than rigid metal at the same nominal size — size flex one increment larger or derate CFM capacity.
Use the Free Calculator
HVAC Duct Size Calculator — online ductulator for round and rectangular duct by CFM.
Duct Friction Rate Calculator — verify friction rate on an existing run.
FAQ
Is there a free online ductulator?
Yes. Our duct size calculator performs the same CFM-to-duct-size lookup as a physical ductulator at standard residential friction rates — no download required.
What is duct u lator?
It is a common misspelling of ductulator — the circular slide-rule or digital tool used to size HVAC ductwork by airflow and friction rate.
Mcquay duct sizer vs online tools
Mcquay (Daikin) duct sizer is the professional desktop standard. Online calculators cover the same math for single-segment sizing; Mcquay adds fitting loss libraries and full Manual D integration.
What friction rate should I use?
0.08–0.10 in.wg per 100 ft for residential supply branches. Manual D divides available blower static across the longest run — do not assume 0.10 on every segment of a large system.