Sunscreen Calculator — Amount and Reapplication
Estimate a sunscreen amount per application and a simple reapplication schedule.
Formula and sources updated · Data sources · 2View algorithm, constants and default inputs (JSON)
About this calculator
Estimate product quantity using a rough amount per application and a two-hour reapplication schedule. The model does not add extra applications after swimming or sweating; reapply more often when needed and follow the product label. Partial-area amounts are planning estimates, not personal measurements.
Worked example
calculated with the default values below
Coverage Full body · Hours in sun 4 h Amount per application 1.00 oz · Amount per application 29.6 ml · Applications 2 · Total amount 59 ml
Method and assumptions
Q = c × 29.5735; A = max(1, ceil(h ÷ 2)); total = Q × A c is fluid ounces per application: body/children 1, face and neck 0.15, arms 0.35. Partial-area amounts are illustrative. The schedule omits earlier reapplication after swimming or sweating; follow the product label. No SPF or weight input is used. Estimate product quantity using a rough amount per application and a two-hour reapplication schedule. The model does not add extra applications after swimming or sweating; reapply more often when needed and follow the product label. Partial-area amounts are planning estimates, not personal measurements.
Data sources
Disclaimer
These calculators provide planning estimates only. Building codes, wiring regulations and safety requirements differ by country and change over time, and nothing here replaces a licensed professional or a permit. For structural, electrical or gas work, follow local code and have the installation inspected.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
Q = c × 29.5735; A = max(1, ceil(h ÷ 2)); total = Q × A
- c
- Amount per application (US fl oz)
- h
- Hours in sun
- Q
- Amount per application (mL)
- A
- Applications
c is fluid ounces per application: body/children 1, face and neck 0.15, arms 0.35. Partial-area amounts are illustrative. The schedule omits earlier reapplication after swimming or sweating; follow the product label. No SPF or weight input is used.
Frequently asked questions
How should I interpret the total sunscreen amount?
The total is amount per application × max(1, ceil(exposure hours ÷ 2)). Four hours gives two modeled applications; just over four gives three. Body and child presets are 1 US fl oz per application, face/neck 0.15 and arms 0.35. Partial-area and child presets do not adjust to individual size. Swimming or sweating can require earlier reapplication; follow the label.
Which inputs and limits apply to Sunscreen Calculator — Amount and Reapplication?
Use the units shown beside each field. These are form limits, not recommended settings. Hours in sun: 0.5–12 h Q = c × 29.5735; A = max(1, ceil(h ÷ 2)); total = Q × A c is fluid ounces per application: body/children 1, face and neck 0.15, arms 0.35. Partial-area amounts are illustrative. The schedule omits earlier reapplication after swimming or sweating; follow the product label. No SPF or weight input is used. Estimate product quantity using a rough amount per application and a two-hour reapplication schedule. The model does not add extra applications after swimming or sweating; reapply more often when needed and follow the product label. Partial-area amounts are planning estimates, not personal measurements.
What is a complete worked example for Coverage = Full body; Hours in sun = 4 h?
Inputs: Coverage = Full body; Hours in sun = 4 h. Calculation: Q = c × 29.5735; A = max(1, ceil(h ÷ 2)); total = Q × A. Results: Amount per application = 1.00 oz; Amount per application = 29.6 ml; Applications = 2; Total amount = 59 ml.