If I bought at least 51% of all the stock of company “X”, would I become owner? Also, can company “X” refuse to sell these shares to me? How could I, Joe Avg, know how many shares to buy to equal 51%? Is it 51% of the estimated worth of company “X” published in some Standards & Poors book, maybe?
Somewhere in a company’s annual report you’ll find “Shares Outstanding” which will tell you how many there are.It will even tell you the largest individual (or institutional) shareholders if you want to concentrate your efforts there first.
If Company X is privately held, yes they can refuse to sell. If it’s publicly-traded, they can’t refuse to sell. Instead, you will deal with thousands/millions of individual investors, pension funds, insurance companies, etc. who can choose to sell or not as they see fit.
The share price is based on the open market. So today, Company X shares may be worth $20, and tomorrow they may be worth $19.50. You’ll have to put in a bid and see if you get any takers.
Once you overcome those hurdles and get 51% of the shares, yes, you own the company, or at least a controlling interest in it.
According to my corporations professor, in most large companies that have been around for a while, 20% is a sufficiently large stake to control a company’s destiny, because the other shares are usually so dispersed.
The way it works is ass so: Shareholders elect the Board of Directors. The Board hires the Preisdent, C.E.O., C.O.O., and other officers. It also decides large questions of corporate policy. Board members are typically elected on a one-share, one-vote basis. Therefore, if you’ve got 51% of the shares, you can fill the Board with your people, including yourself if you wish. If you’ve even got 20%, that’s probably enough to fill most of teh Board; others might be able to get enough votes to put up one or two members, but if they disagree with your people they’ll always be overruled.
Of course this is an oversimplification, but that’s the basics.
–Cliffy
As other people pointed out, you would have a controlling interest. This doesn’t mean you can do whatever you want with the company, though. You still have obligations to the minority shareholders.
Strictly speaking, company “x” doesn’t own its own shares. Those shares are owned by individuals (or other companies), who can choose to sell or not sell them to you. If Company “X” is publicly traded, a common way to start purchasing shares is via the stock exchange.
Another way to purchase shares is via a “tender offer,” which is basically an announcement to the public that you will purchase any and all shares of company “X,” for a certain price, up to 51% of the shares.
Frequently in such situations, senior management will oppose the takeover. (Keep in mind that once the takeover is complete, management will be replaced.) In those situations, management can implement certain “defenses,” for example a so-called “poison-pill.” In those cases, the takeover battle will usually end up in court, and a judge will decide if management’s defense is unreasonable.
So the short answer is, yes, management of Company “X,” can block the sale, but if they behave too unreasonably, you can take them to court over it and continue with the takeover.
As other people pointed out, this information is readily available. You can probably get it on the internet. I believe that the “market capitalization” of an issue is the total number of outstanding shares multiplied by the current price. So if you know the market cap and the current price, you can figure out how many shares you need.
As pointed out by another poster, you don’t necessarily need 51% to have effective control.
One last point: If you are planning to attempt a takeover of a publicly traded company, you might consider consulting with a lawyer. 
As other people pointed out, you would have a controlling interest. This doesn’t mean you can do whatever you want with the company, though. You still have obligations to the minority shareholders.
Strictly speaking, company “x” doesn’t own its own shares. Those shares are owned by individuals (or other companies), who can choose to sell or not sell them to you. If Company “X” is publicly traded, a common way to start purchasing shares is via the stock exchange.
Another way to purchase shares is via a “tender offer,” which is basically an announcement to the public that you will purchase any and all shares of company “X,” for a certain price, up to 51% of the shares.
Frequently in such situations, senior management will oppose the takeover. (Keep in mind that once the takeover is complete, management will be replaced.) In those situations, management can implement certain “defenses,” for example a so-called “poison-pill.” In those cases, the takeover battle will usually end up in court, and a judge will decide if management’s defense is unreasonable.
So the short answer is, yes, management of Company “X,” can block the sale, but if they behave too unreasonably, you can take them to court over it and continue with the takeover.
As other people pointed out, this information is readily available. You can probably get it on the internet. I believe that the “market capitalization” of an issue is the total number of outstanding shares multiplied by the current price. So if you know the market cap and the current price, you can figure out how many shares you need.
As pointed out by another poster, you don’t necessarily need 51% to have effective control.
One last point: If you are planning to attempt a takeover of a publicly traded company, you might consider consulting with a lawyer.