Around 70 percent. That is the whole answer, and it is worth about two minutes of your attention rather than the anxiety it usually attracts.
What is worth understanding is why, because once you know that, you can tell instantly whether your situation is a problem or not.
Humidity is about the cork, not the wine
The wine inside a sealed bottle has no idea what the humidity is. Glass is not permeable. Nothing about the air in your cellar touches the liquid.
What the air touches is the cork. And a cork is a seal that only works while it stays swollen.
Store a bottle in air that is too dry and the outer face of the cork gives up moisture and shrinks. The seal loosens, oxygen works its way in, and the wine oxidises. It happens slowly, over months and years, and you find out on the day you open it, which is the worst possible day to find out.
That is also the real reason bottles are stored lying down. It is not tradition and it is not about saving space. A bottle on its side keeps the wine against the inner face of the cork, so the cork stays wet from the inside whatever the room is doing. Screwcap and glass-stoppered bottles do not need it, and you can stand those up quite happily.
What goes wrong at each end
Below about 50 percent: corks dry, shrink and lose their seal. This is the failure that costs you wine, and it is the reason the number exists at all.
Above about 80 percent: the wine is still perfectly fine, but everything around it is not. Labels foxing, mould on the label edge, cardboard cases collapsing, and a musty room. If you ever intend to sell or gift a bottle, a ruined label costs real money, because provenance is partly a visual judgement.
Between 50 and 80: nothing bad is happening. This is a much wider comfort zone than most articles imply, and 70 is a target rather than a threshold.
Why nobody publishes a number
Look for a humidity specification on a wine cabinet and you will mostly not find one. Manufacturers say “maintains ideal humidity” and leave it there.
There are two honest reasons for that. A sealed cabinet with a cooling coil naturally condenses moisture and returns some of it, so humidity is a by-product of the design rather than something actively controlled. And it varies with how often you open the door, how full the cabinet is and what the room is doing, so a single number would be close to meaningless.
The practical consequence: this is not a specification you can shop on. It is a reason to buy a cabinet built for wine rather than a drinks fridge, and then to stop thinking about it.
When you actually need to check
A purpose-built cabinet: do not worry about it. Holding humidity is part of what the money bought.
A converted cupboard, garage or spare room: worth checking, because you have no control at all. A hygrometer costs very little and tells you in a week whether you have a real problem.
A basement: the classic too-damp case rather than too-dry. Basements often sit above 80 percent, which is fine for the wine and bad for the labels and the cardboard. A dehumidifier on a low setting fixes it, and a basement that already sits at 10 to 14 °C may mean you do not need a powered cabinet at all, just racking.
A heated room in winter: the genuinely risky one. Central heating pulls indoor humidity down hard, sometimes to 30 percent, and a rack of bottles standing in a warm dry living room is the worst combination on this page: dry air, warm air and light.
The short version
Aim for 70, do not panic anywhere between 50 and 80, and store bottles on their side so the cork stays wet from the inside regardless.
If your bottles are in a proper cabinet, this is already handled and temperature is the number that deserves your attention instead. If they are in a room you converted yourself, spend a few pounds on a hygrometer before you spend anything else.
The full set of criteria is in our wine cellar buying guide.
Frequently asked questions
What humidity should a wine cellar be?
Around 70 percent. Below roughly 50 percent corks dry out and shrink, which lets air into the bottle. Above roughly 80 percent labels and cardboard start to suffer, along with anything else in the room. Most purpose-built cabinets hold this range on their own.
What happens if a wine cellar is too dry?
The cork dries from the outside and shrinks, which breaks the seal and lets oxygen in. That is slow and irreversible: the wine oxidises, and you usually only discover it on opening. It is also the single reason bottles are stored on their side, so the wine keeps the inner face of the cork wet.
Do I need a humidifier in my wine cellar?
Almost certainly not if you have a purpose-built cabinet, because holding humidity is part of what you paid for. A converted room or a basement is different, and a cheap hygrometer will tell you in a week whether you have a problem worth solving.
