Mold Cleanup Calculator: DIY or Call a Pro?
The EPA’s rule of thumb is simple. If the moldy area is smaller than about 10 square feet, roughly a 3-by-3-foot patch, most homeowners can clean it up themselves. Bigger areas, heavy water damage, contaminated water and mold in the heating or cooling system call for a professional. Measure each patch, tick what applies, and the calculator adds up the area and tells you where you stand.
Fix the moisture first
Mold needs water. Cleaning it off without stopping the leak, the condensation or the damp air only means it grows back. The EPA’s guidance:
- Fix leaks and dry water-damaged materials and belongings within 24–48 hours.
- Keep indoor relative humidity below 60%, ideally between 30% and 50%.
- Vent bathrooms, kitchens and clothes dryers to the outside.
If water is coming through a ceiling right now, start with what to do when water is leaking from the ceiling. For damp basements and closets, see whether a dehumidifier helps with mold.
When to call a professional
- More than about 10 sq ft of mold, or a lot of water damage. The EPA points to its guide for larger cleanups, and most people hire a remediation company at this point.
- Sewage or other contaminated water. The EPA recommends a professional who has experience with that kind of damage.
- Mold in the heating, ventilation or air-conditioning system. Don’t run the system if you suspect it is contaminated. Mold can spread through the whole house.
- Health concerns. If anyone in the home has asthma, allergies, breathing problems or a weakened immune system, talk to a doctor before starting.
- A musty smell with no visible source, which can mean mold inside walls or under floors. See how to find the source of a mold smell.
If you hire a company, ask which guidelines it follows, such as the EPA’s or those of a professional organization, and check references. The work should include finding and fixing the moisture source, not just removing what you can see.
If you clean it yourself
- Protect yourself: wear an N-95 respirator, long gloves that reach the middle of your forearm, and goggles without ventilation holes.
- Hard surfaces: scrub the mold off with detergent and water, then dry the surface completely. The EPA does not recommend chlorine bleach as a routine method.
- Porous materials: ceiling tiles, carpet, insulation and moldy drywall may have to be cut out and thrown away. Mold can grow in the gaps and pores where cleaning can’t reach.
- Don’t paint or caulk over mold. Clean and dry the surface first.
- Keep others out of the room while you work, especially children and anyone with health concerns.
Room-by-room guides: mold on walls, mold on a bathroom ceiling, mold in the shower and mold on wood.
Common questions
How do I measure a mold patch?
Measure the length and width of the visible growth, including the faint edges, and multiply. For several separate spots, measure each one; the calculator adds them up. A 3 ft × 3 ft patch is 9 square feet, just under the EPA’s 10 sq ft line.
Is black mold more dangerous than other mold?
Color doesn’t tell you how risky a mold is, and the same cleanup rules apply to all of them. See black mold vs mildew.
Do I need a mold test?
Usually not. The EPA says that when mold is visible, sampling is generally unnecessary. You already know it is there and needs to be removed. Testing can help when you smell mold but can’t find it.