# Hot Spring Mixing and Soak Time Calculator

Work out how much cold stream water to mix into a hot pool for a target temperature, and get a cautious soak-time guide.

- URL: https://toolstackhub.co.uk/tools/hot-spring-mixing-and-soak-time-calculator/
- Category: Calculators
- Price: free, no sign-up
- Privacy: runs in the browser; input is not uploaded
- Last updated: 2026-10-08

## About
Natural hot springs are often hotter than is comfortable or safe. This calculator shows how much cold water to blend with the hot water to reach a target temperature, using the simple mixing formula, and then gives a cautious guide for how long to stay in water at that temperature. Enter temperatures in °C or °F. The soak guide is general safety information, not medical advice, and it errs on the side of caution.

## How to use
1. Choose °C or °F.
2. Enter the temperature of the hot pool, the cold stream or tap water you can mix in, and the temperature you want.
3. Read what share of hot and cold water to use, and the amount of each per 10 litres, plus a cautious soak-time note.
4. Check with a thermometer and adjust. Real temperatures change as the water cools.

## FAQ
**How hot is too hot for a hot spring?** A common upper limit for hot tubs is 104 °F (40 °C). Many natural springs exceed this and need cooling or very short soaks.

**How long should I soak?** A common cautious guide is 10 to 15 minutes at around 104 °F, with breaks. Get out if you feel dizzy or unwell.

**How do I mix hot and cold water to a target temperature?** Hot share = (target − cold) ÷ (hot − cold). The rest is cold water.

**Is the Hot Spring Mixing and Soak Time Calculator free?** Yes, with no sign-up or limits.