Compost Calculator

• •Use the Compost Calculator when you need accurate results quickly without the risk of manual computation errors or unit conversion mistakes.
• •Use it to verify calculations made by hand or in spreadsheets — an independent check can catch errors before they lead to costly decisions.
• •Use it to explore how changing input parameters affects the output — a quick way to develop intuition and identify the most influential variables.
• •Use it when collaborating with others to ensure everyone is working from the same numbers and applying the same assumptions.

The compost calculator determines how much compost you need to top-dress or amend a garden bed, raised bed, or landscape area. Adding compost is one of the most effective ways to improve soil structure, increase water retention in sandy soils, enhance drainage in clay soils, and supply a slow-release source of essential plant nutrients. Most extension services recommend applying 1 to 3 inches of compost annually to existing beds and 4 to 6 inches when building new garden beds. This calculator converts your bed dimensions and desired application depth into cubic feet and cubic yards so you can order the right amount from a bulk supplier or determine how many bags to buy from a garden center.

• !Mixing up inches and feet for the depth — 2 inches is only 1/6 of a foot.
• !Underestimating volume for irregularly shaped beds — measure the longest and widest points and accept a slight over-order.
• !Applying uncomposted (fresh) organic matter, which can rob nitrogen from the soil during decomposition.