The supply of insurance available to meet demand. Capacity depends on the industry's financial ability to accept risk. For an individual insurer, the maximum amount of risk it can underwrite based on its financial condition. The adequacy of an insurer's capital relative to its exposure to loss is an important measure of solvency.

A property/casualty insurer must maintain a certain level of capital and policyholder surplus to underwrite risks. This capital is known as capacity. When the industry is hit by high losses, such as after the World Trade Center terrorist attack, capacity is diminished. It can be restored by increases in net income, favorable investment returns, re insuring more risk and or raising additional capital. When there is excess capacity, usually because of a high return on investments, premiums tend to decline as insurers compete for market share. As premiums decline, underwriting losses are likely to grow, reducing capacity and causing insurers to raise rates and tighten conditions and limits in an effort to increase profitability. Policyholder surplus is sometimes used as a measure of capacity.