# Duct Calc — HVAC Duct Sizer

> Round, rect & flex duct sizing

Canonical page: [https://chrome-stats.com/d/id6792500757](https://chrome-stats.com/d/id6792500757)

## Overview

- **ID:** `id6792500757`
- **Platform:** Apple
- **Type:** Apple app
- **Status:** Available
- **Publisher:** Gun woo Kim
- **Category:** Productivity
- **Version:** 1.0.1
- **Last updated:** 2026-08-03
- **First published:** 2026-07-29
- **Size:** 29 MB
- **Data as of:** 2026-09-20
- **Store listing:** [Apple App Store](https://apps.apple.com/us/app/duct-calc-hvac-duct-sizer/id6792500757)
- **Privacy policy:** [https://cleverlywittyapps.notion.site/Privacy-Policy-3a2c235088498138aa46d9894a4a2d05](https://cleverlywittyapps.notion.site/Privacy-Policy-3a2c235088498138aa46d9894a4a2d05)

## Description

Size ductwork in seconds — round, rectangular, and yes, flex.

Duct Calc is an offline HVAC duct calculator built for techs and designers who need answers on the job, not another subscription.

FREE, FULLY WORKING
• Duct sizing (equal friction, round) — enter CFM and friction rate (in. w.c./100 ft), get the exact diameter, the stock size to grab, and the velocity in FPM
• Unit converter — airflow, velocity, and duct area. CFM · L/s · m³/h at one tap

PRO (ONE-TIME PURCHASE)
• Flex duct sizing — friction based on published research data (fully stretched to 30% compressed). Compressed flex loses far more pressure than the charts admit; Duct Calc corrects for it
• Rectangular conversion — equivalent diameter to W×H (1-inch increments), with aspect-ratio warning
• Airflow back-calc — know the duct, get the CFM: from round diameter or rectangular W×H, by velocity or friction rate
• Register / diffuser selection — neck size, free area, and throw estimate from CFM and neck velocity
• Static pressure — straight-run loss plus fittings (elbows, tees, transitions), totaled in in. w.c.

BUILT FOR THE FIELD
• 100% offline — works in the attic, the crawlspace, the mechanical room
• Big touch targets, screen stays awake, no account, no sign-in
• Your inputs never leave the device

ONE-TIME PURCHASE
The free version is fully functional — round sizing and conversion are never crippled. One purchase unlocks everything else, forever.

No subscription. No ads. No features taken away later.

Calculations follow standard practice (Darcy–Weisbach / Colebrook friction, ASHRAE equivalent-diameter equation, published flex-duct compression data). Reference only — verify final designs against applicable codes and manufacturer data.

## Rankings

- #2,045,116 — Overall

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Source: [Chrome-Stats](https://chrome-stats.com/d/id6792500757)