How much sunscreen do you need? A complete guide for face and body

June marks the official start of summer, and you can see it everywhere. People go on longer walks, terraces are full and children are playing outside for hours again.

During these months, sun protection becomes more important than ever. However, a study published found (Skin Exam, 2024) that most people tend to apply only 25–50% of the amount of sunscreen they need. This results in a significant drop of the effectiveness of SPF, even with high protection like SPF 30 or 50.

The issue is not just about daily application, but about using the right amount. Too little product simply means less protection than you think.

In this guide, Team Altruist explains exactly how much sunscreen you need for optimal protection during the summer months.

Why the right amount of sunscreen matters

Sunscreen only works properly when applied in sufficient amounts, which equals around 2 mg per cm² of skin. In practice, most people apply far less, which significantly reduces the level of protection.

A good thing to keep in mind is to apply a visible layer, similar to the thickness of peanut butter spread on toast. In other words: be generous.

Not using enough sunscreen can lead to:

Increased risk of sunburn: even if you think you’re well protected, a thin layer can still lead to redness and burning.
Faster skin ageing: UV radiation breaks down collagen and elastin, leading to fine lines, wrinkles, and loss of firmness.
Pigmentation spots: the skin may react unevenly to UV damage, causing dark spots or discolouration.
Higher risk of skin cancer: long-term, cumulative UV damage increases the risk of skin cancer.

In short: too little sunscreen = too little protection.

How much sunscreen should you use?

A good rule of thumb is to apply a visible and generous layer, similar to the thickness of peanut butter spread on toast. In other words: don’t be shy with it.

How much sunscreen do you need for your face?

The face is one of the most exposed parts of your body and receives UV radiation daily, even when it’s cloudy.

That’s why it’s crucial to wear sunscreen daily, as well as using the correct amount.

The two-finger rule

The easiest and most common method is the two-finger rule.

Apply two lines of sunscreen along your index and middle finger. This amount is enough to properly protect your face and neck, and is widely recommended because it’s simple and visual.

The teaspoon rule

A more technical method is the teaspoon rule.This equals around ½ a teaspoon (2–2.5 ml) for the face and neck combined.

How long does a tube of face sunscreen last?

When used daily, sunscreen runs out faster than most people expect.

The Altruist Face Fluid is specifically designed around this recommended dosage. When applied properly, a 50 ml tube typically lasts around 3 to 4 weeks.

Its lightweight texture and non-greasy finish make it easy to use every single day, without feeling heavy on the skin or leaving a white cast. This is especially important for facial sunscreen, as comfort plays a major role in whether people actually apply enough product.

How much sunscreen do you need for your body?

In addition to the face, the body also requires adequate sun protection, to cover all exposed skin. A helpful guideline from the NHS is the “7 teaspoons rule” NHS, 2026).

This means an average adult should apply: