Free calculator Air sample volume and indoor-to-outdoor ratio
Work out a spore trap sample's air volume from the pump rate and time, and compare indoor results with the outdoor control. The calculator compares; it never decides a pass or fail.
Reading results against the outdoor control
Outdoor spore levels change with the season, the weather and the time of day, so an indoor count means little on its own. Assessors take an outdoor control at the same visit and compare each indoor sample with it, both in total and type by type, and with the same area before remediation.
What counts as clearance is written into the protocol or remediation plan before work starts. Clearwright shows the comparison next to your own criteria; the decision stays with the licensed assessor.
What the states require
| State | Licences | Paperwork |
|---|---|---|
| Texas (TDLR) | Separate assessment and remediation licences; a TDLR-licensed lab for samples | Written protocol to the client at least one day before work, with clearance criteria. Remediation notice to TDLR at least 5 days before work from 25 contiguous sq ft. Chain of custody for samples. Passed clearance report or final status report. TDLR complaint notice on reports. |
| New York (DOL) | Separate assessor and remediation licences | Mold remediation plan before work (from more than 10 sq ft) with clearance criteria, estimated cost and timeline. Post-remediation assessment with a passed clearance report or final status report. |
| Florida (DBPR) | Separate mold assessor and mold remediator licences | Applies from more than 10 sq ft. A signed contract is required; the report format is set by professional practice. |
| Washington DC (DOEE) | Mold assessor and remediator licences by exam | Mold assessment report with a protocol where needed, the remediator's work plan, and a verification report within 10 days after remediation. |
A summary for orientation, not legal advice. Rules change; check the current rules with the state regulator.
Questions
How do I calculate the air volume of a spore trap sample?
Multiply the pump's flow rate by the sampling time: 15 liters per minute for 5 minutes is 75 liters, or 0.075 cubic meters. Calibrate the pump and record the rate and time with each sample.
Why take an outdoor air sample?
The outdoor sample is the control. Indoor counts mean little on their own because outdoor levels change with season, weather and time of day, so assessors compare each indoor sample with an outdoor sample taken at the same visit.
What indoor-to-outdoor ratio passes clearance?
There is no single number. Clearance criteria are set by the assessor in the protocol or remediation plan before work starts, and Texas requires them to be written into the protocol. The calculator shows the comparison; your criteria decide.
Can the same company assess and remediate a mold job?
Not on the same project in Texas, New York or Florida, where assessment and remediation are separately licensed and kept apart. Check the rules in your state.
What goes in a passed clearance report in Texas?
Observations, the locations of measurements and samples, temperature, humidity and material moisture readings, the lab results, the photos and a clear statement that the area passed. A final status report is issued when it does not.
Not affiliated with any state regulator, laboratory or certification body. This page makes no health claims and sets no thresholds.