Mask vs. No Mask Calculator

Estimate how much wearing a mask lowers infection risk by combining the source person's outward filtration with your mask's inward filtration, then project that risk across repeated exposures.

Quick Facts

Model
Independent multiplicative filtration
Exposure remaining = (1 - source outward efficiency) x (1 - receiver inward efficiency).
Direction matters
Source vs. receiver efficiency differ
The same mask type typically blocks outgoing droplets better than it filters incoming air, except well-fitted N95/KN95.
Repeated exposure
Risk compounds over events
Cumulative risk over n events = 1 - (1 - per-event risk)^n.

Your Results

Calculated
Exposure reduction from masks
-
Combined source + receiver filtration
Per-exposure risk, with masks
-
vs. baseline without masks
Cumulative risk, no masks
-
Across all exposure events
Cumulative risk, with masks
-
Across all exposure events

Ready

Set the baseline risk, mask types, and number of exposures, then calculate.

About the Mask vs. No Mask Calculator

This calculator models how much a mask - worn by the potentially infected person, by you, or by both - reduces the amount of infectious aerosol or droplets that reach you, compared with wearing no mask at all. It uses the standard independent-filtration approach: each mask blocks a percentage of particles, and two masks in series combine multiplicatively rather than by simple addition.

How the calculation works

  • Source control: a mask on the potentially infected person blocks a share of what they exhale. This is the "outward" filtration efficiency.
  • Receiver protection: a mask on you blocks a share of what you inhale. This is the "inward" filtration efficiency.
  • Combined effect: the fraction of exposure that still reaches you is (1 - outward efficiency) x (1 - inward efficiency). Subtracting that fraction from 1 gives the total exposure reduction.
  • Risk scaling: the calculator multiplies your entered baseline (no-mask) infection risk by that remaining exposure fraction to estimate the per-exposure risk with masks. This assumes infection probability scales roughly with received dose, a reasonable approximation when the per-exposure risk is modest.
  • Cumulative risk: across multiple independent exposures, the chance of at least one infection is 1 - (1 - per-event risk)^(number of exposures), applied separately to the no-mask and with-masks scenarios.

Putting the result in context

The outward and inward filtration percentages in this tool are approximate, commonly cited ranges for each mask category, not a measurement of any specific product. Actual performance depends heavily on fit, material, and how consistently a mask is worn, so treat the output as a directional estimate of relative benefit rather than a precise probability.

When to consult a professional

This tool performs a transparent risk-reduction calculation for education and planning. It is not a substitute for guidance from a healthcare provider or public health authority, especially for people at elevated risk from infection or when deciding on protection in a specific clinical or occupational setting.

Frequently Asked Questions

What formula does the Mask vs. No Mask Calculator use?
It uses the standard multiplicative filtration model: the fraction of exposure that still reaches you equals (1 minus the source mask's outward filtration efficiency) multiplied by (1 minus your mask's inward filtration efficiency). Multiplying that fraction by an assumed baseline (unmasked) infection risk gives the estimated per-exposure risk with masks.
Why do the source mask and the receiver mask use different efficiency numbers?
A mask worn by the potentially infected person mainly blocks exhaled droplets and aerosol leaving that person (source control), while a mask worn by the exposed person mainly filters what they inhale (receiver protection). Fit and design affect these two directions differently, so outward and inward efficiency for the same mask type are treated as separate model inputs.
What does the cumulative risk over multiple exposures mean?
If a single exposure carries a probability p of infection, the calculator estimates the chance of at least one infection across n independent exposures as 1 minus (1 minus p) raised to the power n. This compounding is why a small per-event risk can still add up to a much larger risk over repeated contacts, and why consistent masking matters over time.

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