The conversion ratio is the number of common shares that each share of preferred stock turns into when it converts, and it starts at one-to-one but adjusts for events like down rounds and stock splits. It sets how much common each preferred share becomes.

Founders care because the conversion ratio decides how many common shares investors end up with, which drives ownership and dilution at conversion.

How the conversion ratio works

Most preferred stock converts into common stock. This happens on events like an IPO or by investor choice. The conversion ratio tells you how many common shares each preferred share yields.

The starting point is almost always one-to-one. One share of preferred converts into one share of common. The ratio is usually expressed through a conversion price stated in the charter. Dividing the original issue price by that conversion price gives the number of common shares per preferred share.

What changes the conversion ratio

Two main forces move the conversion ratio away from one-to-one. The first is a stock split or stock dividend. The charter adjusts the ratio so a split does not dilute or unfairly enrich preferred holders.

The second is anti-dilution protection. If the company later sells stock at a price below what earlier investors paid, anti-dilution provisions lower the conversion price. A lower conversion price raises the conversion ratio. The preferred holder then receives more common shares, which increases their dilution impact on founders.

The as-converted basis

Many rights and calculations use an “as-converted” view. As-converted means you count preferred as if it had already converted into common at the current ratio. Voting, ownership percentages, and payout math often run on this basis.

The mechanics live in the certificate of incorporation, not in a statute. Read the conversion terms in the charter before you close a priced round. A ratio that looks like a formula today can shift real ownership tomorrow.

This is general information, not legal advice.