About UL Sleep System Calculator
Helping ultralight backpackers make informed gear decisions since 2026.
To provide free, reliable tools that help backpackers understand their sleep system's true performance and make better gear decisions.
We were tired of guessing whether our gear would keep us warm. So we built the tool we wished existed when planning our own trips.
We combine established formulas from the UL community with personal experience factors to give you practical, real-world estimates.
The Story Behind the Calculator
If you've ever spent a cold night on the trail, shivering despite your "20-degree rated" sleeping bag, you know the frustration of temperature ratings that don't match reality.
Temperature ratings are complicated. Manufacturers use different testing standards. Personal variation is huge. And that's before you factor in your sleeping pad, what you're wearing, and dozens of other variables.
We built UL Sleep System Calculator to cut through this complexity. Our tools combine:
- Established formulas from the ultralight community, including the Enlightened Equipment quilt layering calculation
- R-value science based on the ASTM F3340-18 testing standard
- Real-world adjustments for clothing layers and personal warmth tendencies
The result is a practical estimate that accounts for factors most temperature charts ignore. Is it perfect? No calculator can predict exactly how warm you'll feel. But it's a much better starting point than manufacturer ratings alone.
Disclaimer
Our calculators provide estimates based on general principles and community-tested formulas. Actual comfort varies based on many factors including humidity, wind, shelter design, individual metabolism, fatigue, and more.
Always err on the side of caution, especially for critical trips. Bring backup warmth options and know the signs of hypothermia. No app can replace good judgment and experience.
Have questions, suggestions, or found an error in our data? We'd love to hear from you.
contact@ulsleepsystem.com