The hours are the easy part
An hour in the oven is six to eight on low. Two hours is eight to twelve. Every conversion chart online gives you that table and stops, and the table is fine. It is also not what goes wrong.
What goes wrong is that an oven recipe and a slow cooker recipe are written for two different physical situations, and only one of them loses liquid.
Nothing boils off under a sealed lid
A slow cooker sits below boiling with a heavy lid on it. Steam rises, hits the cold lid, condenses and runs straight back into the pot. At the same time the meat and the vegetables give up their own water, which has nowhere to go either. A lot of dishes finish with more liquid in them than went in.
An oven or hob recipe was written expecting to lose a good share of its liquid over the cook. That reduction is doing real work: it is what turns stock into sauce. Move the recipe across unchanged and the meat is perfect and the sauce is dishwater, which is the single most common disappointment with a slow cooker and it is completely avoidable.
Cut the liquid by about a third going in, and add nothing extra unless the recipe genuinely needs it to cover the ingredients. If it still looks thin at the end, take the lid off for the last half hour on high.
Low and high are the same temperature
This is the fact that makes sense of the two-to-one rule and almost nobody knows it. Both settings settle at roughly the same place, somewhere around a bare simmer at 90 to 95 degrees. They differ in how fast they climb there, not in where they finish.
So an hour on high is about two hours on low, and the further into a long cook you get, the less the choice matters, because both have been sitting at the same temperature for hours. Low is the sensible default if you are going out, since it gives the timing more room to be wrong in your favour.
Nothing browns in there
Browning is a chemical reaction between sugars and proteins that needs a surface well above the boiling point of water. The inside of a slow cooker never gets close and never will, so the pan step is not an optional flourish somebody added to look professional. It is the only opportunity the whole dish has to develop that flavour.
Meat and onions, ten minutes, in the pan you were going to wash anyway. Deglaze it with some of the liquid and tip that in too, because the browned material stuck to the pan is the part you were making.
What goes in at the end
Four things want holding back, and they fail in four different ways.
Dairy splits. Cream, milk and soft cheese cannot take hours of heat, and once split there is no recovery. Last half hour.
Fresh herbs vanish. They give everything up in the first hour and then contribute nothing at all. Dried herbs are the opposite and want the whole cook, which is why slow cooker recipes look like they were written by somebody who prefers dried.
Pasta and rice turn to paste. Starch in liquid for eight hours is a description of wallpaper paste. Cook them separately, or add near the end and watch.
Prawns and white fish go rubbery. They cook in minutes and then keep cooking. Twenty minutes at the end is plenty.
Two habits worth changing
Root vegetables at the bottom. Most people put the meat in first because it feels like the main event. The heat comes from the sides and the base, so the bottom of the pot is the hottest part, and carrots and potatoes take longer than most braising cuts. Putting the slow things where the heat is solves both at once.
Leave the lid alone. Every look lets out the heat and the steam, and the pot is slow to recover by design. Reckon on twenty to thirty minutes added each time.
And the one that is not about results: never put frozen meat in. A slow cooker warms up gently on purpose, so frozen meat crawls through the temperature range bacteria like best for hours before it reaches anywhere safe. Defrost it in the fridge first.
Common questions
How do I convert an oven recipe to a slow cooker?
Roughly, an hour in the oven is six to eight hours on low or three to four on high, and a two hour braise is eight to twelve on low. That is the easy half and it is all most charts give you. The half that decides how it turns out is the liquid: cut it by about a third, because nothing evaporates under a sealed lid, and brown the meat in a pan first, because nothing browns inside the pot.
Why is my slow cooker sauce watery?
Because almost nothing boils off. The lid seals, the pot sits below boiling, and any steam that rises hits the lid, condenses and runs straight back in. Meanwhile the meat and vegetables give up their own water with nowhere to send it, so a lot of dishes finish with more liquid than they started with. An oven recipe was written expecting to lose a good share, so moving it across unchanged leaves you short of about a third of the reduction.
Is low or high better on a slow cooker?
They reach the same temperature, which is the fact that makes sense of everything else. Both settle at roughly a bare simmer, somewhere around 90 to 95 degrees, and the difference is how fast they climb there rather than where they end up. So an hour on high is about two on low, and on a long cook the choice barely matters. Low is the safer pick if you are going out, because there is more room for the timing to be wrong.
Do I have to brown meat before slow cooking?
If you want it to taste of anything much, yes. Browning is a reaction that needs a surface well above boiling and a slow cooker never gets close, so the pan is the only opportunity the dish has to develop that flavour at all. It is the step people skip on a weekday and it is the single biggest reason a slow cooker meal can come out tasting flat and grey rather than deep and savoury.
Can you put frozen meat in a slow cooker?
No, and this is the one genuine safety point rather than a matter of results. A slow cooker is designed to warm up gently, so frozen meat spends hours passing slowly through the temperature range where bacteria multiply fastest before it ever reaches a safe cooking temperature. Defrost it fully in the fridge first. Everything else on this page is about how the food turns out; this one is not.
Where do the vegetables go in a slow cooker?
Root vegetables at the bottom, meat on top, which is the opposite of what most people do. The heat comes from the sides and the base, so the bottom of the pot is the hottest part, and carrots and potatoes take longer than most braising cuts of meat. Putting the slow things where the heat is fixes both halves of the problem at once, and it stops the meat sitting in the hottest spot for eight hours.
When do I add cream or milk to a slow cooker?
In the last half hour. Hours of heat splits dairy, and once it has split nothing brings it back. The same timing suits fresh herbs, which give up everything they have in the first hour and then taste of nothing, and soft cheese. Dried herbs are the opposite case and want the whole cook to open up, which is why slow cooker recipes read as though somebody had a preference for dried.
How do I thicken a slow cooker stew?
At the end rather than the start. Flour or cornflour stirred in early sits in liquid for hours and can go grainy or split, so it is better to take the lid off for the last half hour on high and let some of it go, or stir in a slurry and give it twenty minutes. Starting with a third less liquid, as this tool suggests, removes most of the need for either.
Does opening the lid matter?
More than you would expect. Lifting it lets out the heat and the steam that has been doing the work, and a slow cooker is slow to recover by definition. The usual figure is twenty to thirty minutes added to the cook every time you look. On a dish that is already eight hours long that is survivable; on a shorter one it is the difference between dinner at seven and dinner at eight.