DRESS FOR THE WATER
What Wetsuit Do I Need?
Find a starting thickness for the sea temperature, then understand the fit and conditions behind the choice.
Start with the water
Use the sea temperature at your beach, rather than the air temperature. A forecast temperature is a model estimate.
How this guide works
We use the Celsius rows in O’Neill’s published thickness guide. Its whole-degree rows are broad reference bands: for example, 12°C up to just below 18°C uses the row labelled 12–17°C. They are not precise biological boundaries. Decimal inputs near a boundary deserve a look at both neighbouring rows. Fahrenheit converts using (°F − 32) × 5 ÷ 9.
See every temperature band
| Water temperature | Published starting options |
|---|---|
| 4–7°C | 5/4 mm or 6/5 mm |
| 8–11°C | 4/3 mm or 5/4 mm |
| 12–17°C | 3/2 mm or 4/3 mm |
| 18–20°C | 2 mm wetsuit or shorty |
| 21–25°C | 1 mm wetsuit |
| 26°C and above | UV shirt or rash vest |
Fit, wind and time in the water
A loose suit can flush with cold water. A suit that restricts breathing or normal movement is not a good fit either. Wind, air temperature, activity, seams, lining and wear affect comfort. Your warmth and session answers change the advice; they never change the published bands.
When to get local advice
This tool covers a general adult reference range of 4–30°C. Ask a qualified instructor or specialist about children, unusual conditions and temperatures outside that range. Do not use a calculator to decide how long it is safe to stay in cold water. End a session if you are becoming cold or unwell.
Keep learning
How to rinse, dry and store a wetsuit · Choose your first surf session · Find a starting surfboard volume
Sources
- O’Neill: wetsuit thickness and water temperature
- O’Neill US reference chart and its limits
- RNLI: surfing equipment and local assessment
Written by BestSwell using the linked sources. No hands-on product test or individual fitting is claimed.