The Shadow Rule: A No-App Trick to Gauge UV Intensity Anywhere
No phone, no app, no UV meter, just look at your shadow to know instantly when the sun is strong enough to burn you.
According to the EPA's shadow rule, if your shadow is shorter than your height, the sun is high enough that UV exposure is intense and protection is needed.
The EPA promotes the shadow rule as an accessible companion to the UV Index, noting that a short shadow signals the sun is high in the sky, when UV radiation peaks and protection matters most.
Questions we get a lot
How does the shadow rule work?
Look at your shadow on the ground. If it's shorter than you are tall, the sun is high in the sky and UV exposure is intense, so you need protection. If your shadow is longer than your height, the sun is lower and UV is weaker. It's the EPA's quick, screen-free way to read the sky.
Is the shadow rule as reliable as checking the UV Index?
The shadow rule is a handy estimate of how high the sun is, which correlates with UV intensity, but it doesn't account for factors like altitude, cloud cover, ozone, or reflective surfaces. The EPA offers it as a practical backup to the UV Index, not a replacement. When you can, check the index for a more precise forecast.
Can I use the shadow rule to teach my kids about sun safety?
Yes, it's well suited for that. Children can easily grasp 'short shadow means strong sun, time to cover up.' The EPA presents it precisely because it's memorable and needs no equipment, making it an easy habit to build on hikes, at the beach, or in the backyard.
r/CampingandHiking: 'Is there a reliable way to judge how strong the sun is on the trail without checking my phone every hour?'