Sometimes we have to get in through a lock in a hurry, and there's never anything worse than having to do so when we have a huge rack of keys and no idea which is the right one for the lock. Whether it's a friend's house we're trying to get into, or you have simply forgotten which of your own keys work with which lock, this can be a serious problem. In a real emergency then it is advisable to call a locksmith. Locksmiths work with enough keys and have enough industry expertise that they should be able to immediately recognise which key is for which lock. However even if they do not manage to successfully find the correct key, they will at least be able to pick the lock or get in other ways.
Of course it would be preferable, cheaper and quicker if you could forego using a locksmith, which in this scenario is more an option for emergencies. Thus, if you have the time, you should first try to identify the keys and what they're for yourself. Here we'll look at some pointers you can use to help you find the right key.
First of all, look at the make of the key. If the make is the same as the lock, then this is already a good bet that the two go together. For instance if the key says 'Yale' on it, and you know that the lock is a Yale lock, then you should try these together. This won't always be the case as if the key is copied, then this will likely mean that it bears the name of the company that copied it rather than the name of the original key.
Another way to tell is of course through the shape and the size. Normally the size of the key will basically reflect the size of the key hole. You can tell from the keyhole right away if the key is a cylinder key or a lever key - as the former will have a crooked slit for a blade, while the latter will have a hole for putting in the long end of a lever key (the more old fashioned looking keys with a handle and a long neck).
Likewise just the size has a bearing - larger and more important locks for instance will have larger sturdier keys, so if the key is very small or light then this is more likely to be for a small padlock or something similar.
Keys for the front door almost always have some things in common. They are almost always for instance cylinder keys, so the key will be small with a round handle and a blade coming right out of it. At the same time keys for the front door will often be coloured - if you have a key chain and randomly one of the cylinder keys is blue then this is quite likely the one for the front door (or the porch). This is precisely so that the owner can find it quickly and easily. Finally if one of the keys has a rubber grip on it, then this too may be for the front door as it suggests that the key is used very regularly.
This should help you to narrow down, if not identify the key you need. Failing these attempts however you will need to use a locksmith.