Editor's note

SPF labelling is tested at 2mg per square centimetre of skin. Your face and neck together cover roughly 600 square centimetres. The maths produces a quarter-teaspoon — about 1.25ml — as the minimum for face and neck combined. Most people apply the two fingers across a single fingertip. That's roughly a quarter of the required amount, which gives you an effective SPF of 5 to 8, not 30 or 50.

What the two-finger rule actually measures

The two-finger rule asks you to dispense product along the length of your index and middle fingers — both fingers, full length, from knuckle to fingertip. That produces roughly 1ml to 1.25ml for an average-sized adult face and neck. The quarter-teaspoon weight test (0.25 tsp on a kitchen scale) gives the same target for people who want precision over estimation.

Myth, meet fact

• Myth: A 'little dab' of SPF is enough for the face. Fact: A little dab is roughly 0.25ml. The tested minimum for face and neck is 1.25ml. That's a fivefold gap.
• Myth: Applying more SPF than the two-finger amount wastes product. Fact: Applying more than needed is fine. Applying less results in a lower effective protection factor than the label states.
• Myth: Reapplication is optional if you're inside most of the day. Fact: Reapplication matters when you're exposed to daylight — windows pass UVA regardless of cloud cover.

Start here, if SPF quantity is new to you

1. Why your SPF probably isn't working (3 min)
2. The two-finger rule — how to do it correctly (3 min)
3. The quarter-teaspoon test (3 min)
4. SPF over makeup — the reapplication question (5 min)
5. Which SPF format works best for your skin type (4 min)

Everything on SPF application

• Why your SPF 50 is working like an SPF 8
• The two-finger rule — the correct version
• Quarter-teaspoon test — how to calibrate your dose
• Reapplying SPF over makeup — what actually works
• Tinted SPF — does the colour change the coverage?