How much sunscreen to apply

For an adult, about one ounce — a shot glass — covers the whole body. For face and neck, about a quarter teaspoon, or the two-finger measure. Reapply every two hours and immediately after swimming or toweling off. Most people apply between a quarter and a half of the amount SPF is measured at, and protection falls faster than the amount skipped.

This is the single most useful page on this site, and it costs nothing to act on. An SPF 30 applied properly outperforms an SPF 50 applied thinly.

The measures, by body area

Two consequences follow immediately. A 4-ounce bottle is four full-body adult applications — so a bottle that lasts a family all summer is evidence of under-application, not efficiency. And buying the larger tube is a protection decision, not just an economy.

The two-finger measure, for faces

Squeeze a line of sunscreen along the full length of your index finger, then another along your middle finger. That is roughly a quarter teaspoon, and it is the amount for face and neck together. Most people apply well under half of it, largely because the full amount looks like more product than they want on their face.

If the correct amount looks unacceptable on your skin, the answer is a different product rather than less of this one. A tinted or lighter formula applied fully beats an elegant one applied thinly.

Why under-applying costs more than it seems

SPF is measured in a laboratory at 2 milligrams per square centimeter of skin, spread evenly. A filter layer protects the skin it is actually covering — so a thinner layer is not a uniformly weaker shield but a patchier one, with more skin effectively uncovered.

The result is that halving the dose does not halve the SPF; it reduces effective protection by considerably more. Which is why the SPF 30 versus SPF 50 question matters far less than this one does.

The spots everyone misses

• Ears, especially the tops and the rims.
• The back of the neck, and the part in your hair.
• The tops of the feet, painful in sandals and consistently forgotten.
• Lips, which need an SPF balm rather than lotion.
• Under swimsuit straps that shift as you move.
• Behind the knees and the backs of the legs.
• Eyelids and under the eyes — a stick is the right tool here.
• Hands, which get more cumulative sun than almost anywhere else.

Applying it so it works

1. Apply to dry skin, 15 to 30 minutes before going out if you are using a chemical formula.
2. Dispense the full amount first, then spread. Squeezing as you go guarantees you stop early.
3. Work in sections — one limb at a time — rather than trying to cover everything at once.
4. Two thin layers beat one thick one for evenness and appearance.
5. Reapply every two hours, and immediately after swimming or toweling off. A reapplication is a full second coat, not a top-up.

Making it realistic

An ounce per person per application, four times a day, for a family, is a lot of sunscreen — which is exactly why people quietly ration it. Two things genuinely help.

Buy value formats. Price per ounce decides whether you are generous. And reduce the area. A UPF 50+ shirt removes the torso from the calculation entirely, which cuts both the volume and the reapplication workload by most of the body.