Construction Formula API

Free, open REST API for construction material calculations. No API key required. Returns JSON with formulas, results, and helpful notes.

Free — No API Key CORS Enabled GET & POST

Quick Start

GET Request

curl "https://buildcalcpro.org/api/calculate/concrete?length_ft=10&width_ft=10&thickness_in=4"

POST Request

curl -X POST "https://buildcalcpro.org/api/calculate/concrete" \
  -H "Content-Type: application/json" \
  -d '{"length_ft": 10, "width_ft": 10, "thickness_in": 4}'

Response

{
  "success": true,
  "calculator": "concrete",
  "inputs": {
    "shape": "slab",
    "quantity": 1,
    "length_ft": 10,
    "width_ft": 10,
    "thickness_in": 4
  },
  "results": {
    "volume_cubic_feet": 33.33,
    "volume_cubic_yards": 1.23,
    "volume_cubic_meters": 0.9439,
    "bags_80lb": 56,
    "bags_60lb": 74
  },
  "formula": "Volume (cu yd) = (Length_ft × Width_ft × Thickness_in ÷ 12) ÷ 27",
  "notes": "Add 5-10% extra for waste and spillage."
}

Available Calculators

Concrete

Volume in cubic yards, bags (80lb & 60lb) for slabs, footings, columns.

Endpoint

GET /api/calculate/concrete

Parameters

Parameter	Required	Description
`length_ft`	required	Length in feet (slab/footing)
`width_ft`	required	Width in feet (slab/footing)
`thickness_in`	optional	Thickness in inches (default: 4)
`shape`	optional	slab \| footing \| column \| cylinder
`diameter_in`	optional	Diameter in inches (column/cylinder)
`height_in`	optional	Height in inches (column/cylinder)
`quantity`	optional	Number of shapes (default: 1)

Try it

/api/calculate/concrete?length_ft=10&width_ft=10&thickness_in=4

Roofing

Shingle bundles, squares, underlayment rolls, ridge caps.

Endpoint

GET /api/calculate/roofing

Parameters

Parameter	Required	Description
`length_ft`	required	Building length in feet
`width_ft`	required	Building width in feet
`pitch`	optional	Roof pitch, e.g. 4/12 (default: 4/12)
`waste_pct`	optional	Waste percentage (default: 10)

Try it

/api/calculate/roofing?length_ft=40&width_ft=30&pitch=4/12

Drywall

Sheets, joint tape, compound, and screws for any room.

Endpoint

GET /api/calculate/drywall

Parameters

Parameter	Required	Description
`length_ft`	required	Room length in feet
`width_ft`	required	Room width in feet
`height_ft`	optional	Ceiling height (default: 8)
`include_ceiling`	optional	true/false (default: false)
`sheet_size`	optional	4x8 or 4x12 (default: 4x8)
`doors`	optional	Number of doors (default: 0)
`windows`	optional	Number of windows (default: 0)

Try it

/api/calculate/drywall?length_ft=12&width_ft=12&height_ft=8&doors=1&windows=2

Paint

Gallons and liters of paint for room walls.

Endpoint

GET /api/calculate/paint

Parameters

Parameter	Required	Description
`length_ft`	required	Room length in feet
`width_ft`	required	Room width in feet
`height_ft`	optional	Ceiling height (default: 8)
`doors`	optional	Number of doors (default: 0)
`windows`	optional	Number of windows (default: 0)
`coats`	optional	Number of coats (default: 2)

Try it

/api/calculate/paint?length_ft=12&width_ft=12&height_ft=8&coats=2

Tile

Tiles and boxes needed with grout gap and waste factor.

Endpoint

GET /api/calculate/tile

Parameters

Parameter	Required	Description
`room_length_ft`	required	Room length in feet
`room_width_ft`	required	Room width in feet
`tile_length_in`	optional	Tile length in inches (default: 12)
`tile_width_in`	optional	Tile width in inches (default: 12)
`grout_gap_in`	optional	Grout gap in inches (default: 0.125)
`waste_pct`	optional	Waste percentage (default: 10)

Try it

/api/calculate/tile?room_length_ft=12&room_width_ft=10&tile_length_in=12&tile_width_in=12

Gravel

Tons and cubic yards for driveways and landscaping.

Endpoint

GET /api/calculate/gravel

Parameters

Parameter	Required	Description
`length_ft`	required	Area length in feet
`width_ft`	required	Area width in feet
`depth_in`	optional	Depth in inches (default: 4)
`gravel_type`	optional	pea-gravel \| crushed-stone \| river-rock \| etc.

Try it

/api/calculate/gravel?length_ft=20&width_ft=10&depth_in=4&gravel_type=crushed-stone

Insulation

Depth, volume, rolls/bags based on R-value target.

Endpoint

GET /api/calculate/insulation

Parameters

Parameter	Required	Description
`area_sqft`	required	Area to insulate (sq ft)
`target_r_value`	optional	Target R-value (default: 38)
`insulation_type`	optional	fiberglass-batt \| blown-cellulose \| spray-closed \| etc.

Try it

/api/calculate/insulation?area_sqft=1500&target_r_value=38

Mulch & Soil

Cubic yards and bags for garden beds.

Endpoint

GET /api/calculate/mulch

Parameters

Parameter	Required	Description
`length_ft`	required	Bed length in feet
`width_ft`	required	Bed width in feet
`depth_in`	optional	Depth in inches (default: 3)
`material`	optional	mulch \| topsoil \| compost \| gravel \| sand

Try it

/api/calculate/mulch?length_ft=10&width_ft=10&depth_in=3&material=mulch

Brick & Block

Bricks/blocks and mortar bags for walls.

Endpoint

GET /api/calculate/brick

Parameters

Parameter	Required	Description
`wall_length_ft`	required	Wall length in feet
`wall_height_ft`	required	Wall height in feet
`brick_type`	optional	standard-brick \| modular-brick \| cmu-8 \| cmu-12
`waste_pct`	optional	Waste percentage (default: 10)

Try it

/api/calculate/brick?wall_length_ft=20&wall_height_ft=8&brick_type=standard-brick

Lumber

Board feet and linear feet for lumber pieces.

Endpoint

GET /api/calculate/lumber

Parameters

Parameter	Required	Description
`thickness_in`	optional	Thickness in inches (default: 2)
`width_in`	optional	Width in inches (default: 4)
`length_ft`	optional	Length in feet (default: 8)
`quantity`	optional	Number of pieces (default: 1)

Try it

/api/calculate/lumber?thickness_in=2&width_in=4&length_ft=8&quantity=10

AI Agent Integration

This API is designed for AI agents, chatbots, and LLMs that need to perform construction calculations. Every response includes the formula used and contextual notes to help AI provide accurate answers.

OpenAPI Spec

Download the OpenAPI 3.0 specification for tool integration:

/api/openapi.json

LLM Discovery

Our llms.txt file includes API documentation for AI crawlers.