Tent listings throw waterproof numbers at you: 1,200 mm, 3,000 mm, 8,000 mm. It's natural to assume the biggest number means the driest night.
It doesn't, and once you know what to look past, choosing gets simple. Emma spent weeks getting rained on to show why: she slept in 11 tents, mostly through hail, sleet, rainforest rain and Scottish squalls, and the rating on the box was a poor guide to who stayed dry.
Below you'll find what the numbers mean, the four things Emma learned about ratings in real storms, and how much rating you actually need.
What a Tent Waterproof Rating Means
A tent's waterproof rating is its hydrostatic head: the height of a column of water, in millimeters, that the fabric holds back before water starts to come through. A 1,500 mm rating means the fabric held back a column of water 1.5 meters tall in the test.
Makers quote one figure for the fly and often a higher one for the floor, because the floor faces a different kind of pressure.
Four Things Emma Learned in Real Storms
1. 1,200 mm is usually enough, if the design is right
The Sea to Summit Telos TR2 Plus has a fly rated only 1,200 mm. Because its raised ridge stops water pooling, it shrugged off 18 hours of squalls on the Isle of Skye. The same 1,200 mm on a delicate floor is a different story: Emma warns it will seep if you pitch in a puddle and kneel on it.
2. Fabric stretch matters more than the number
The NEMO Dagger OSMO's fly is rated 2,000 mm, and Emma called it magic. Standard nylon stretches up to 4% when wet, so the fly sags, touches the inner mesh and wicks water through. The Dagger's OSMO fabric, and heavy polyester like the MSR Elixir 2's, stayed drum-tight all night.
3. A high rating can't fix bad design
The Naturehike Cloud Up 2 is rated 4,000 mm, twice the Dagger's fly. It still let water in, because its budget seam tape and a front door that unzips over the floor let water pool and drip inside.
4. Ground pressure is the real enemy
Sitting or kneeling on wet ground pushes water up through a floor with far more force than rain hitting a fly. That's why Sea to Summit gives the Telos an 8,000 mm floor, and on a saturated bog on Skye, Emma says that 8,000 mm saved her: no groundwater came through even when she knelt on it.
High ratings can't fix bad design.
Emma, our tent tester
How Much Waterproof Rating Do You Need?
- Fly: on a well-designed tent, 1,200 mm can be enough, as the Telos showed. Shape, tension and seams matter more than going higher.
- Floor: more is worth having, because kneeling and sitting load it. If you camp on wet ground, a high-rated floor like the Telos's 8,000 mm, or a groundsheet, protects you where the pressure is.
- Fabric type: in long rain, a fly that doesn't stretch (polyester, or blends like OSMO) beats a higher-rated nylon fly that sags.
Is It a Leak or Condensation?
Usually condensation. The first mistake on Emma's list is a tent with its vents zipped shut on a cold night, where the water on the walls came from the people inside. Before you blame the rating, open the vents and check whether the fly is touching the inner tent.
Waterproof Rating FAQ
Is 3,000 mm waterproof enough for a tent?
For a fly, usually yes, if the tent is well designed. Emma's test showed design matters more: a 1,200 mm fly stayed dry in Scottish squalls while a 4,000 mm budget tent dripped at the door.
Why is a tent floor rated higher than the fly?
Because people kneel, sit and lie on it, which presses water up through the fabric. Rain landing on a fly pushes far less hard. The Telos floor is rated 8,000 mm for exactly this reason.
Does a higher rating mean a better tent?
No. In Emma's 11-tent test, a 4,000 mm fly let water in at the door, while the tent that stayed dry through 18 hours of Scottish squalls had a 1,200 mm fly. See our best backpacking tents for how each one did.
The Bottom Line
Treat the waterproof rating as a minimum, not a ranking. Past about 1,200 mm on the fly, the shape, the fabric's stretch, the seams and the doors decide whether you stay dry. Put the high numbers where the pressure is: the floor. For more on choosing, see our tent buying guide.
Editor's Note, 17 October 2026: New guide, from Emma's notes on how 11 tents' waterproof ratings held up in real rain, hail and sleet.
Our Testers
This guide was edited by Sean Williams and tested by Emma Williams.
- Sean Williams, Editor-in-Chief. Sean built the team of researchers and testers behind our reviews and sets the rule the site runs on: we buy what we test, and we say what we found.
- Ryan Williams, Lead Tester. Ryan tests our family and basecamp tents, inflatables, generators and emergency gear.
- Emma Williams, Editor and Tester. Emma leads our backpacking tent testing, mostly in wet weather.
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