𧬠COVID Event Risk Estimator
A simplified educational model. Assumptions stated, not hidden.
Simplified educational model with illustrative assumptions, not an epidemiological measurement. Follow current public health guidance.
How risky is that wedding, flight, or dinner? This estimator combines the five variables that actually drive airborne transmission, setting, crowd size, duration, masks, and your immunity, into one relative risk number. It is a simplified educational model with its assumptions printed on the box, inspired by the microCOVID project. It ranks activities against each other; it does not predict whether you will get sick.
How to Use This Estimator
Describe the event honestly. The relative risk score updates live.
Pick the setting, from crowded indoor to open outdoor.
Enter the number of people in close contact and the hours you will spend with them.
Set masks and your protection level, then compare scenarios: the same event outdoors vs indoors is the instructive comparison.
The Model and Its Assumptions
Every number in the model is a stated simplification. The 1 percent prevalence assumption is the load-bearing one: during a surge, multiply your mental answer several-fold; during a lull, divide. The setting factors encode the aerosol science: outdoors dilutes virus enormously, ventilation matters indoors, crowding multiplies contacts. Mask factors reflect that good masks on you protect you substantially even when others are unmasked. Immunity factors reflect that recent boosters and prior infection cut infection risk, though less against newer variants.
What the model omits: distance details, talking vs silent (talking emits far more aerosol), the infectiousness of the specific variant, your age and health (see the mortality estimator for that half), and waning immunity timing. Use the output to compare options, not to certify safety. A "lower" score is genuinely lower risk; it is not zero risk.
Worked Example
Two hours in a typical indoor restaurant with 20 people around, most masked except while eating, recent booster: 20 x 2 x 0.3 x 0.4 x 0.5 x 0.01 = 0.024 expected infectious contacts in model units, scaled to 240 risk units: moderate. Move it outdoors, uncrowded: setting factor drops from 0.3 to 0.01, and the score falls 30-fold to single digits. Wear an N95 instead: another ~2.7-fold cut. The model's lesson is the hierarchy: setting first, then masks, then duration and crowd size. Changing the biggest factor beats optimizing the small ones.
What Actually Moves the Needle
Outdoors is the single biggest lever: the dilution factor is so large that outdoor events rarely drive transmission. Ventilation is the indoor equivalent: open windows, HEPA filters, and avoiding the crowded bar area. Fit-tested N95s protect the wearer well even solo; surgical masks help mostly as source control. Shorter is better, linearly: two hours is twice one hour. And staying home when symptomatic, plus testing before gathering with vulnerable people, remains the highest-value behavior in the whole repertoire.
Risk tolerance is personal and contextual: a young boosted person visiting vaccinated friends faces a different calculus than someone visiting an 85-year-old on chemotherapy. Layer the mitigations to match the stakes: the event you cannot skip gets the N95 and the outdoor table; the optional crowded indoor event during a surge gets skipped. Models inform; values decide.
Honest Limits
This is not the microCOVID project (which its creators wound down) and not an epidemiological instrument: it is a teaching model with round-number assumptions. Real transmission depends on the variant, the actual prevalence that week (check your local wastewater or hospitalization data), and individual biology. Public health guidance, not this page, sets policy. What the page does well is build intuition for the hierarchy of controls, which is the durable lesson no variant takes away.
Related Calculators
Keep exploring: try our COVID mortality risk and BMI calculator for the next piece of the picture.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
How do you estimate COVID risk for an event?
Combine setting, crowd size, duration, masking, and immunity. This estimator multiplies them into relative risk units with stated assumptions (e.g., 1% prevalence). It ranks scenarios against each other; it does not predict individual infection.
What was the microCOVID project?
A volunteer-built tool that estimated COVID infection risk in "microCOVIDs" (millionths of a chance) from activity data and local prevalence. Its creators wound it down as the pandemic evolved. This page is a simplified educational successor, not the original.
Is it safe to eat indoors at a restaurant?
Risk depends on prevalence, ventilation, crowd, duration, and your vulnerability. Outdoor dining is far lower risk. During surges, or before visiting vulnerable people, choose outdoor, off-peak, or takeout. There is no universal safe/unsafe line.
Do masks still help with new variants?
Yes. Well-fitting N95/KN95 masks substantially cut the wearer's inhaled dose even against newer variants; surgical and cloth masks help more as source control. Fit matters as much as material.
How much does being outdoors reduce COVID risk?
Enormously: outdoor dilution cuts aerosol concentration by orders of magnitude versus indoors. In this model the outdoor factor is 30-100x lower than crowded indoor. It is the single biggest lever available.
Does a recent booster reduce infection risk?
Yes, substantially in the first months, with protection against infection waning faster than protection against severe disease. Boosters remain the best tool against hospitalization and death for vulnerable groups.
Should I test before visiting elderly relatives?
Yes, when prevalence is high or anyone is vulnerable: a rapid test the day of the visit catches many infectious cases. Combine with ventilation and masking for layered protection. No single layer is perfect.
How long are you contagious with COVID?
Typically from ~2 days before symptoms through ~8-10 days after onset for most people, longer if immunocompromised. Rapid tests correlate reasonably with infectiousness: positives mean take precautions.
What is the biggest factor in event risk?
Setting (indoor crowded vs outdoor) dominates, then masks, then duration and crowd size. Moving an event outdoors or wearing an N95 each cut risk several-fold; halving the guest list helps less than either.
Is this estimator scientifically validated?
No. It is a simplified educational model with illustrative assumptions, not a validated epidemiological tool. Use it to build intuition about relative risk, and follow current public health guidance for decisions.