In economics, the law of supply states that quantity supplied usually rises when a good’s price rises, all else equal.
A higher selling price can make additional production profitable, encouraging firms to use more labor, machinery, materials, or operating time. This is normally shown by an upward-sloping supply curve. A fall in price generally produces the opposite movement along that curve.
The condition “all else equal” excludes changes in production costs, technology, taxes, subsidies, the number of sellers, and sellers’ expectations. Those factors can shift the supply curve rather than merely causing movement along it.
Supply responses vary by industry and time period. Farmers may be unable to expand output quickly during one growing season, while factories may adjust more readily. Thus, the law describes direction, not a fixed size of response.