.sqm

The Squaremetry plan format (.sqm)

The Squaremetry format is an open JSON file (.sqm) for floor plans measured to a standard. It holds floors, walls with their kind and thickness, doors and windows, rooms with their use and ceiling heights, voids, stairs and outbuildings, and where each size came from. Every length is a whole number in 0.1 mm. Areas under a standard are optional and always come with the rule set and its version. The specification is CC BY 4.0; the JSON Schema and a small reader are MIT.

schemaVersion 1
Specification CC BY 4.0, schema and reader MIT
File .sqm, media type application/vnd.squaremetry+json

Download the JSON Schema Check a file

A small example

One room of 4 by 5 m inside the walls, with a door, and the area stored when the file was saved: 20 m² of usable area under the Dutch measuring instruction, rule set 0.1.5.

one-room.sqm

{
  "format": "squaremetry-plan",
  "version": 1,
  "savedAt": "2026-10-01T09:00:00.000Z",
  "project": {
    "schemaVersion": 1,
    "id": "example-one-room",
    "name": "One room",
    "units": "metric",
    "normProfile": "nl-meetinstructie-2019-07",
    "floors": [
      {
        "id": "f1",
        "name": "Ground floor",
        "level": 0,
        "elevation": 0,
        "defaultHeight": 26000,
        "walls": [
          {
            "id": "s1",
            "a": {
              "x": -1500,
              "y": -1500
            },
            "b": {
              "x": 41500,
              "y": -1500
            },
            "thickness": 3000,
            "kind": "exterior",
            "prov": {
              "src": "laser",
              "tol": 20
            }
          },
          {
            "id": "s2",
            "a": {
              "x": 41500,
              "y": -1500
            },
            "b": {
              "x": 41500,
              "y": 51500
            },
            "thickness": 3000,
            "kind": "exterior",
            "prov": {
              "src": "laser",
              "tol": 20
            }
          },
          {
            "id": "s3",
            "a": {
              "x": 41500,
              "y": 51500
            },
            "b": {
              "x": -1500,
              "y": 51500
            },
            "thickness": 3000,
            "kind": "exterior",
            "prov": {
              "src": "measured"
            }
          },
          {
            "id": "s4",
            "a": {
              "x": -1500,
              "y": 51500
            },
            "b": {
              "x": -1500,
              "y": -1500
            },
            "thickness": 3000,
            "kind": "exterior",
            "prov": {
              "src": "measured"
            }
          }
        ],
        "rooms": {
          "f:s1+s2+s3+s4": {
            "name": "Living room",
            "fn": "living",
            "highest": 26000
          }
        },
        "holes": [],
        "openings": [
          {
            "id": "o1",
            "wallId": "s1",
            "kind": "door",
            "at": 21500,
            "width": 9000,
            "swing": "left-in"
          }
        ]
      }
    ]
  },
  "derived": {
    "ruleSet": {
      "id": "nl-meetinstructie-2019-07",
      "version": "0.1.5"
    },
    "computedAt": "2026-10-01T09:00:00.000Z",
    "main": {
      "key": "GOW",
      "area": 2000000000
    },
    "totals": {
      "GOW": 2000000000,
      "GOOI": 0,
      "GOGB": 0,
      "OEBR": 0
    }
  }
}

What is in a file

A file is a small wrapper around the plan. The plan is the source; everything else can be computed from it again.

What is in a file
Field	What it holds
format, version	Always "squaremetry-plan" and 1: this is a Squaremetry file, wrapper version 1.
savedAt	When the file was saved (UTC). Optional.
project.schemaVersion	The version of the plan inside: 1. A reader brings older versions up to date (see Versions).
project.units, normProfile	The units the user works in (metric or imperial) and the measuring profile: nl-meetinstructie-2019-07, us-ansi-z765-2021, de-woflv-2004, es-rd515-1989 (Spain: usable and built area), fr-carrez-1996 (France: private area under the Carrez law), fr-boutin-2009 (France: living area under the Boutin law), ca-ab-rms-2024 (Alberta, Canada: the Residential Measurement Standard, a proposal under review), it-superficie-commerciale (Italy: commercial area under DPR 138/1998, annex C), or none (floor area inside the walls, no national standard). normChosen: true when the user chose the profile. rmsForm: detached, attached or apartment, the property form for ca-ab-rms-2024 (empty = detached). itCategory: house, villino or villa, the type of home for it-superficie-commerciale (empty = an ordinary home; for a villino or villa the garden counts only above five times the main rooms). commonPermille: the share of common areas in per mille, only for Spain.
project.floors[]	Floors with level, elevation and default ceiling height. Each floor has walls, rooms, holes, openings, stairs and outdoor spaces.
walls[]	A wall from a to b on its centre line, with kind (exterior, party, loadbearing, nonbearing, half, railing), thickness, optional height, layers and prov.
rooms{}	Rooms keyed by their id. The shape of a room follows from the walls; the file keeps what is known about it: name, use (fn), highest ceiling, sloped ceiling, heated, finished, parts under 1.5 m and above 2.0 m.
holes[]	Stairwells, voids, shafts, lifts, setbacks, columns and niches. The standard decides whether they are subtracted.
openings[]	Doors, windows and openings in a wall, with width, swing, sill and height.
stairs[], outdoor[], buildings	Stairs (they count nowhere themselves), balconies and terraces, and outbuildings as their own buildings.
prov	Where a size came from: measured, laser, drawing, scan or assumed, with an optional tolerance.
derived	Optional: the areas computed when the file was saved, with the rule set and its version.

Units

Every length and every point is a whole number in 0.1 mm: 1 m is 10,000, 1 ft is 3,048 and 1 inch is 254. Areas are whole square units of 0.1 mm: 1 m² is 100,000,000. There are no decimal numbers for sizes, so a plan reads the same everywhere and rounding never creeps in.

Points use x to the right and y down, as in the drawing. A wall runs from a to b on its centre line; the room inside gets the inside size.

Areas under a standard

The file may store the areas the Squaremetry engine found when it was saved, under derived: the headline area (GOW under the Dutch rules, GLA under ANSI Z765, WOHNFLAECHE under the WoFlV, UTIL for Spain, SURFACE for France (Carrez and Boutin), AREA without a national standard), every total, the rule set with its version and fingerprint, and when it was computed.

These numbers are never the source. Change the plan and they are out of date: measure again. A reader shows them with the rule set and version, so everyone can see which rules were applied. The rule sets are our own reading of each standard, in our own words; we do not publish a new measuring standard.

Address and privacy

A plan needs no address. Only the details of a measuring report may hold one (project.survey), and only when the user types it. Files have no names of owners, no coordinates and no photos unless the user adds them to the plan.

Versions and migrations

format and version describe the wrapper; project.schemaVersion describes the plan. A change that would make an older file invalid gets a new schemaVersion and a migration: a reader brings an older file up to date step by step before it checks it. Older files always stay readable.

A file from a newer version is never guessed at: the reader says it needs an update. New optional fields can come within a version; readers ignore what they do not know.

How it relates to other formats

The .sqm file is the source. The other formats are exports or a way in, each made from the same plan:

How it relates to other formats
Format	Relation
FML	An export for listing portals that ask for it (one file with all floors). It has no measuring standard; the area goes in the description.
DXF	Export and import of the drawing as lines on layers, for CAD. A DXF has no rooms or standards; on import it becomes a draft plan you check.
IFC 4	Export for BIM: every room an IfcSpace with its area under your standard in the property set Squaremetry_MeasuredArea. Import reads walls, doors, windows and rooms.
RoomPlan	A room scan from an iPhone or iPad with LiDAR (JSON or USDZ). Import only: it becomes a draft of this format that you check.
glTF, GLB, USDZ, OBJ	Exports of the 3D model, for AR and 3D programs. One way only: they have no rooms or standard.

Why it is open

You can always take your plans with you: the file is yours and any program can read it. Portals, agents and other tools can read and write it without asking us. And there was no open format for floor plans that are measured to a standard: this one keeps the facts every standard needs (heights, wall kinds, use, heated, finished, above or below grade).

What is not open: the measuring engine, the editor and the AI. The format makes them more useful, it does not replace them.

File type

Extension .sqm, media type application/vnd.squaremetry+json (our proposal; not yet registered). A .sqm file is JSON in UTF-8, so application/json also works.

HTTP

Content-Type: application/vnd.squaremetry+json
Content-Disposition: attachment; filename="plan.sqm"

License and name

This specification is licensed under CC BY 4.0: use and adapt it, also commercially, and credit Squaremetry. The JSON Schema and the reader are MIT. The name Squaremetry is not part of either license: say that your tool reads or writes the Squaremetry format, but do not call your product Squaremetry or suggest we checked your measurements. A changed format needs its own name and format value.

Example files

Every example home as a .sqm file, with its area and rule set. Open one in the editor with File, Open a file.

Home, Area in the file, Rule set
Home	Area in the file	Rule set
Villa with garden	225.29 m² GO	nl-meetinstructie-2019-07 0.1.5
Small house	1,097.25 sq ft GLA	us-ansi-z765-2021 0.3.0
Ranch house	1,717.25 sq ft GLA	us-ansi-z765-2021 0.3.0
Two-bedroom apartment	983.25 sq ft GLA	us-ansi-z765-2021 0.3.0
Studio apartment	551.25 sq ft GLA	us-ansi-z765-2021 0.3.0
Bungalow	1,296.25 sq ft GLA	us-ansi-z765-2021 0.3.0
Townhouse	1,674.05 sq ft GLA	us-ansi-z765-2021 0.3.0
Colonial house	2,308.5 sq ft GLA	us-ansi-z765-2021 0.3.0
Tiny house	220.5 sq ft GLA	us-ansi-z765-2021 0.3.0
Barndominium	1,899.23 sq ft GLA	us-ansi-z765-2021 0.3.0
Farmhouse	2,892.5 sq ft GLA	us-ansi-z765-2021 0.3.0
Garage apartment	766.85 sq ft GLA	us-ansi-z765-2021 0.3.0
Two-story house	2,220.5 sq ft GLA	us-ansi-z765-2021 0.3.0
One-story house	1,770.25 sq ft GLA	us-ansi-z765-2021 0.3.0
Cottage	869.25 sq ft GLA	us-ansi-z765-2021 0.3.0
Craftsman house	1,867.25 sq ft GLA	us-ansi-z765-2021 0.3.0
A-frame house	796.25 sq ft GLA	us-ansi-z765-2021 0.3.0
Duplex	1,770.25 sq ft GLA	us-ansi-z765-2021 0.3.0
2-bedroom house	1,154.25 sq ft GLA	us-ansi-z765-2021 0.3.0
Log cabin	822.56 sq ft GLA	us-ansi-z765-2021 0.3.0
Mid-terrace house	88.74 m² GO	nl-meetinstructie-2019-07 0.1.5
End-terrace house	132.21 m² GO	nl-meetinstructie-2019-07 0.1.5
Semi-detached house	133.86 m² GO	nl-meetinstructie-2019-07 0.1.5
Detached house	168.78 m² GO	nl-meetinstructie-2019-07 0.1.5
Apartment (upper floor)	77.04 m² GO	nl-meetinstructie-2019-07 0.1.5
1930s terraced house	142.95 m² GO	nl-meetinstructie-2019-07 0.1.5

Changelog of the schema

schemaVersion 1 (2026-10-01): First public version: the wrapper (format, version, savedAt), the plan with schemaVersion 1 (floors, walls with kind and thickness, openings, rooms with use and heights, voids, stairs, outbuildings and the source of each size), and optional derived areas with the rule set and its version.

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