Coronavirus Mask Calculator

Estimate how much airborne exposure is blocked when the contagious person and the exposed person each wear a mask, using the standard multiplicative filtration model: exposure fraction = (1 − source efficiency) × (1 − receiver efficiency).

Quick Facts

Model
Multiplicative two-mask filtration
Exposure fraction = (1 − source efficiency) × (1 − receiver efficiency); two masks compound their protection, they do not simply add.
Typical filtration efficiency
Cloth ~30% · Surgical ~65% · N95/KN95 ~95%
Example planning ranges for well-fitted masks; real-world performance varies with material, fit, and condition.

Your Results

Calculated
Exposure reduction
-
Lower exposure vs. no masks at all
Exposure reaching receiver
-
% of unmasked exposure still getting through
Relative dose reaching receiver
-
Same units as your baseline exposure
Protection factor
-
Times lower exposure than no masks

Ready

Choose a mask for each person and set a baseline exposure, then press Calculate.

Understanding the Mask Exposure Calculator

This tool estimates how much airborne exposure is reduced when both the contagious ("source") person and the person being exposed ("receiver") wear a mask. It uses the standard multiplicative filtration model used in aerosol science and public-health communications: each mask independently removes a fraction of the particles passing through it, so the two masks combine by multiplying their pass-through rates rather than by adding their efficiencies.

The formula

For a source mask with filtration efficiency Es and a receiver mask with efficiency Er (both expressed as fractions between 0 and 1):

  • Fraction reaching the receiver: F = (1 − Es) × (1 − Er) — the share of unmasked exposure that still gets through both masks.
  • Exposure reduction: (1 − F) × 100% — how much lower exposure is compared with nobody masked.
  • Relative dose reaching the receiver: F × baseline exposure — the fraction applied to whatever baseline exposure value you enter.
  • Protection factor: 1 ÷ F — how many times lower the exposure is than the no-mask case.

Because the model is multiplicative, a single strong mask does most of the work. A well-fitted N95 on the receiver alone (Er = 0.95) already cuts exposure by 95% even if the source wears nothing, since F = (1 − 0) × (1 − 0.95) = 0.05. Adding a second mask on the source person then shrinks that remaining 5% further — two masks compound, they don't just average.

Typical filtration efficiency ranges

The calculator's mask-type options use commonly cited example ranges for well-fitted masks: cloth masks around 30%, surgical/procedure masks around 65%, and N95/KN95 respirators around 95%. These are planning assumptions, not certified lab measurements — actual performance depends heavily on material, number of layers, and how snugly the mask seals against the face.

Interpreting the result

Compare the exposure reduction and protection factor together. A 90%+ reduction (protection factor of 10× or more) generally comes from at least one high-efficiency mask (surgical or N95). Reductions below 50% usually mean both people are unmasked or wearing lower-efficiency cloth masks. This calculator only models the filtration effect of the two masks — it does not include distance, ventilation, exposure duration, viral load, or vaccination status, all of which also affect real-world transmission risk, so treat the result as one input among several when making personal decisions, and consult a qualified public health source or clinician for individual guidance.

Frequently Asked Questions

How does the two-mask filtration formula work?
The calculator treats each mask as a filter and multiplies their effects: exposure fraction = (1 − source efficiency) × (1 − receiver efficiency). If the contagious person's mask blocks 65% of particles and the exposed person's mask blocks 95%, only 0.35 × 0.05 = 1.75% of the unmasked exposure gets through — a 98.25% reduction, not a simple 65 + 95 addition.
Why does the receiver's own mask matter even if the other person is unmasked?
Because the formula is multiplicative, a well-fitted respirator worn by the exposed person still removes most particles from the air they inhale even when the source efficiency is 0%. For example, no mask on the source plus a 95%-efficient N95 on the receiver still gives a fraction of (1−0) × (1−0.95) = 0.05, a 95% reduction, since the receiver's mask is filtering on the way in regardless of what the other person wears.
What filtration efficiency should I use for each mask type?
This tool uses commonly referenced example ranges for well-fitted masks: about 30% for cloth masks, about 65% for surgical/procedure masks, and about 95% for well-fitted N95 or KN95 respirators. These are planning assumptions, not certified specifications — actual filtration depends on material, fit, and condition, so adjust the inputs if you have better data.
Does this include distance, ventilation, or exposure time?
No. This calculator only models how two masks multiply together to reduce the fraction of airborne particles reaching the exposed person. It does not account for physical distance, room ventilation, contact duration, viral load, or vaccination status, all of which also affect real-world transmission risk. For personal health decisions, follow guidance from a qualified public health source or clinician.

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