WME, wood moisture equivalent, is a moisture-meter reading expressed as the moisture content a piece of wood would have to produce the same meter response, so a single wood-calibrated scale can be used to compare readings across different materials.
What is WME?
Pin-type moisture meters are calibrated against wood, where moisture content has a well-characterized relationship to electrical resistance. When that wood scale is used on drywall, plaster, or masonry, the number it returns is not the true moisture content of those materials; it is a wood moisture equivalent, a relative reading useful for comparison rather than an absolute percentage. A WME of 15 to 20 on framing lumber is roughly the dry-to-borderline range, while sustained readings well above that signal a wetting that supports growth (ASHRAE 160 frames moisture-control limits behind why those thresholds matter). The key is to read WME as relative across a wall, dry reference versus wet spot, not as a literal moisture-content number for non-wood materials.
Why it matters to a mold inspection
WME lets an inspector map a leak by comparison: scan a known-dry area, then the suspect area, and the delta tells the story even when the absolute number is approximate. Treating a WME reading on drywall as if it were true moisture content is a common misread that overstates or understates wetness. The EPA's central point holds, controlling moisture is the whole game, so the value of WME is locating and bounding the wet zone, not producing a precise percentage (EPA, Mold Remediation in Schools and Commercial Buildings). See wood moisture equivalent (WME) and pin vs pinless moisture meters.
MoldMind records each moisture reading with its WME value, location, and surface type, so a relative scan is documented as the comparison it is.
Sources
- ASHRAE 160: moisture-control design criteria that contextualize why elevated moisture readings matter.
- EPA, Mold Remediation in Schools and Commercial Buildings: the objective is locating and controlling moisture, not a precise percentage.