MPAC (Municipal Property Assessment Corporation) calculates above-grade living area using exterior wall-to-wall measurements. That means wall thickness is included. The actual interior living space is typically 5–10% smaller than the MPAC figure. This is standard practice — not an error.

MPAC’s above-grade area does not include the basement — even a fully finished walk-out basement. Attached garages are also excluded. So a house listed at 1,800 sq ft on MLS might have 2,400+ sq ft of total usable space once you add a finished basement. These are very different value propositions.

The square footage on MLS may come from MPAC records, the listing agent’s own measurements, builder plans, or seller estimates. MLS does not independently verify area figures. If square footage materially affects your decision (rental income projections, price-per-sqft analysis), always ask for confirmation or have it measured by your home inspector.

Every Ontario homeowner can view their property details for free at aboutmyproperty.ca — including recorded square footage, year built, and room counts. If you believe an error exists, the deadline to file a free Request for Reconsideration (RfR) is March 31 of the taxation year (Assessment Act s.39.1(1.1)); only a supplementary or omitted assessment, or the first year of a province-wide reassessment, gives you 120 days from the notice (s.39.1(1.2), (3)). If unresolved, you can escalate to the Assessment Review Board (ARB).

Arthur’s Tip — Pre-Construction Buyers

MPAC Area: What’s In, What’s Out

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