There are really three parts to this question: (1) How is equity expressed as ownership; (2) Who are the owners/investors; and (3) What percentages do they normally receive.
Equity can mean stock (or shares), although it’s often used to refer to stock options as well. Think of equity as the umbrella term that means an ownership interest whether expressed as stock or not. Shares are one expression of equity, but not the only kind since you can own equity in a non-corporate business or investment property.
Stock options give you the right to buy a certain number of shares at a certain price after a certain amount of time. They do not represent ownership, however, unless your right to buy them has vested. Until then, there’s no equity. You can obtain additional information that clearly and concisely explains how stock options work here.
Stock is a type of equity that’s commonly referred to as an equity investment. When you buy stock as an equity investment, you’re expecting its value to increase and to derive income from its dividends or the profit you make from its sale (capital gains).
Owners & Investors
An angel round of funding is part of the seed round and usually refers to funding below $1 million (although they can somewhat more than that). For this reason, seed rounds for high tech startups usually don’t see angel rounds since large VCs (venture capital firms) tend to offer capital well into the millions of dollars to promising high tech firms.
For the average startup, an angel investor is typically a high net worth individual who provides an emerging company with capital, in exchange for equity (ownership) or convertible debt.
On average, angel investors receive about a 15% post-seed equity position in startup companies. As I said, this is an average, so it can be a bit higher or lower depending on the circumstances and negotiations.
Series A is typically the first level where VCs get involved (unless you’re talking about some of those promising high tech startups where VCs can show up in seed rounds). It’s at this round of funding that you’ll normally see the company’s first valuation.
When VC capital falls between roughly $2 million to $10 million, that usually triggers the Series A. VCs can receive an estimated 10% to 30% ownership stake in the startup in exchange for the funding - although some Series A investors can see ownership equity as high as 50%. Their equity position is expressed in preferred stock (the Series A), which is normally the first series of stock issued after common and common stock options (common being typically distributed to founders, employees, friends & family investors and angels).
Series B is an advanced funding round where startups receive access to even greater amounts of capital from VCs and possibly other institutional investors. In exchange for this round of funding, Series B investors receive an average 33⅓% equity position in the startup, resulting in the proportionate dilution to seed and Series A ownership percentages.
You can get more information from this recent piece I posted, which offers more detailed guidance on how to consider sharing the equity pie with your investors. It’s not intended to provide legal advice, but there’s some pretty helpful information there that will give you a better idea of how to frame the concept of ownership, as well as how to allocate percentages.