Loading page
About this tool
How much sunscreen to apply by body area and when to reapply, from the UV index, your skin type and water resistance.
The Sunscreen Reapplication Calculator works out both halves of using sunscreen properly: how much to put on, and how often to put it on again. The dose uses the teaspoon rule adopted by the Cancer Council Australia and the British Association of Dermatologists — about 5 ml for each of the head and neck, each arm, each leg, the front of the torso and the back — and the interval follows the two-hour standard, tightened to the 40 or 80 minutes your label actually claims once you are swimming or sweating heavily.
Open Sunscreen Reapplication Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Tick only what is uncovered and get millilitres and teaspoons, not vague guidance.
Water-resistance claims of 40 or 80 minutes override the two-hour default when you get wet.
Uses erythemal irradiance of 0.025 W/m² per UV index point and published MED values per skin type.
About 35 ml — roughly seven level teaspoons or a shot glass — covers a whole adult body in swimwear, allocated as one teaspoon each to the head and neck, each arm, each leg, the front of the torso and the back. For face and neck alone that is about 5 ml. Applying less does not scale protection linearly; SPF is measured at 2 mg/cm² and most people apply a quarter to a half of that.
Every two hours of sun exposure as a baseline, and immediately after swimming, towel drying or heavy sweating. If the product claims water resistance, that claim is only valid for the 40 or 80 minutes printed on the label — those are the only two durations the FDA allows a sunscreen to claim.
Not in practice. SPF 30 filters about 97% of UVB and SPF 50 about 98%, a difference far smaller than the loss from applying too thin a layer or letting it rub, sweat and swim off. Treat the SPF-multiplied time this tool shows as a laboratory figure and stick to the reapplication schedule instead.
The WHO advises sun protection from a UV index of 3 upward, extra protection from 8 to 10, and all precautions at 11 or above. Below 3 most people need no protection for short exposures, though cumulative time outdoors still matters and reflective surfaces such as snow, water and sand raise effective exposure.
Add the Sunscreen Reapplication Calculatorwidget to your blog or website — free, responsive, no signup. Just keep the “Widget by AltFTool” credit link visible.
<iframe src="https://www.altftool.com/embed/widget/sunscreen-reapplication-calculator"
title="Sunscreen Reapplication Calculator — free AltFTool widget"
width="100%" height="640" style="border:0;border-radius:12px;overflow:hidden"
loading="lazy" referrerpolicy="no-referrer-when-downgrade"></iframe>
<p style="font-size:12px;margin:4px 0 0">Widget by <a href="https://www.altftool.com/tools/all/sunscreen-reapplication-calculator?utm_source=embed&utm_medium=widget">AltFTool — free online tools</a></p>