Duct sizing for target velocity API

From an airflow CFM and a target velocity (fpm) computes the required cross-sectional area, round-duct diameter, equivalent square side, and the actual velocity for a chosen rounded diameter — to avoid undersized, noisy ducts. Answers 'What duct size do I need for this CFM?', 'What is the air velocity in this duct?'.

Price$0.04per request

MethodPOST

Route/v1/engineering/duct-sizing

StatusLive

MIME typeapplication/json

Rate limit120/minute

Cache0s public

engineeringthermofluidshvacduct-sizingductvelocitycfmventilationductwork

API URLhttps://x402.hexl.dev/v1/engineering/duct-sizing

Integration docs

Example request

{
  "cfm": 400,
  "targetVelocityFpm": 800,
  "actualDiameterIn": 9
}

Example response

{
  "cfm": 400,
  "targetVelocityFpm": 800,
  "requiredAreaFt2": 0.5,
  "requiredAreaIn2": 72,
  "roundDuctDiameterIn": 9.5746,
  "equivalentSquareSideIn": 8.4853,
  "formula": "A = CFM/velocity; d = sqrt(4A/π)",
  "interpretation": "Typical supply-duct velocities: ~700-900 fpm (residential), ~1200-1800 fpm (commercial mains).",
  "actualDiameterIn": 9,
  "actualVelocityFpm": 905.4148
}

Input schema

{
  "type": "object",
  "required": [
    "cfm",
    "targetVelocityFpm"
  ],
  "properties": {
    "cfm": {
      "type": "number",
      "description": "airflow (CFM)",
      "examples": [
        400
      ]
    },
    "targetVelocityFpm": {
      "type": "number",
      "description": "target air velocity (feet/min)",
      "examples": [
        800
      ]
    },
    "actualDiameterIn": {
      "type": "number",
      "description": "chosen round-duct diameter (in) to check actual velocity"
    }
  }
}

Output schema

{
  "type": "object",
  "additionalProperties": true
}