Mask & Respirator Particle Reduction Calculator

A respirator rating or filtration efficiency test tells you what a mask can do in a lab, not what it does on your face, and the difference between those two numbers can be significant. This mask & respirator particle reduction tool helps make that gap visible. You give it the outdoor PM2.5 and the mask you are wearing, and it estimates how much of that pollution still reaches your lungs.

Treat the result as an indication, not a measurement. A calculator like this has to assume a lot, from how well your mask seals to how steady the air around you stays, so the real figure for your face could land well above or below what you see. I have put every assumption in the “How this is calculated” dropdown inside the tool, so you can check exactly what sits behind the number. The intention of this tool is to show a rough visualisation of how useful masks & respirators are at reducing the particles you inhale.

Set your air and your mask below. It all runs in your browser, and nothing you enter goes anywhere.

The maths underneath is simple. Your exposure behind the mask is the outdoor concentration divided by the fit factor, the same logic OSHA uses with its protection factors, so a factor of ten turns 20 micrograms into two. The fit factor is the difficult part. Its value for your face can sit a long way from any preset, because facial hair wrecks the seal, and so does the wrong size or a mask tugged down for a quick phone call. Any of those can quickly turn a well-rated N95 into something far weaker. For this reason, the presets here lean conservative, and your own protection might land higher, or a good deal lower. If you want the full list of what is assumed, along with the studies each preset leans on, it is all in the dropdown inside the tool. None of this replaces a real fit test or a workplace respiratory programme.

Thi is the part that catches people out. For any respirator (not mask), the filter media is probably not your limiting factor, the leak around the edges is. A 5% gap at the seal caps your fit factor at roughly 20 no matter how good the filter is, so a P100 worn loose can lose to an N95 that actually seals. The tool folds both effects into a single fit factor, and the advanced panel lets you pull them apart if you like tinkering.

This estimates PM2.5 and only PM2.5. A particulate mask does nothing about gases, so ozone, or the volatile organics that give wildfire smoke its smell, slip straight past the filter. If gases are your worry, you are into gas-cartridge territory, or better, not being in that air at all. The cigarette-a-day figure is a risk analogy borrowed from Berkeley Earth rather than a literal swap, and it assumes you breathe the same air around the clock.