It happens from time to time, that iGUIDE square footage is compared to square footage from other sources and questions about which one is more accurate arise. There are few factors that must be considered here.
First of all, as with any comparison, apples must be compared to apples. Square footage is just one number that describes a complex structure such as a house and there is more than one way to arrive at that number, depending on which methodology or measurement standard is used. Different methods mainly differ in which spaces are counted as excluded from reported square footage. Differences may also come from how sloped ceilings in attic or shared demising walls are treated.
iGUIDE measurement method is summarized here. iGUIDE method essentially follows the Alberta Residential Measurement Standard (RMS) which currently is the most comprehensive standard in North America. Alberta RMS is based on ANSI Z765-2013 standard for single-family houses and extends it to condos and apartments in multi-family residential buildings. Alberta RMS was created because square footage in municipal tax records proved unreliable as those values are produced without following any prescribed standard and comparisons between any two properties may or may not be comparing apples to oranges.
Secondly, any real measurement has an associated measurement uncertainty or measurement error. iGUIDE camera allows measuring distances to walls to within 1cm uncertainty. For a typical house, this can mean up to 5cm uncertainty across the whole house when several rooms are stacked or about 0.5% for distance measurements for that typical floor size. The resulting uncertainty in square footage will be about 1% (double of the distance uncertainty). Therefore, when comparing iGUIDE square footage to square footage from other sources, any differences smaller than 1% (e.g., 25 sqft for a 2,500 sqft house) are meaningless as they are below the measurement noise and thus must be ignored.
If the difference exceeds 1%, then the measurement uncertainty of the second number must be examined and the combined uncertainty must be used during comparison. For example, if measurement A has 1% uncertainty and measurement B has 3% uncertainty, then the combined uncertanbity is 3.16% (square root of 1% squared plus 3% squared). If the difference between A and B is less than 3.16%, then the two measurements are said to be the same within the measurement uncertainty.
If the second measurement uncertainty is not available, then the iGUIDE measurement must be presumed as the most accurate measurement, as no meaningful comparison can be made.
Both Alberta RMS (residential measurement standard) and BOMA (commercial space measurement standard) call for maximum allowed measurement uncertainty of 2% when reporting square footage measurements. As seen from the above, iGUIDE technology meets and exceeds these requirements.