Estimation plays an important role in cost planning by providing budget figures for decision making. There are two main methods of project estimation: detailed estimation and single rate estimation. Detailed estimation involves taking off quantities from drawings and applying unit rates, while single rate estimation uses an overall rate per ton of steel. Cost planning then uses the estimates to break the project into tasks with durations and resources. Comparing actual costs to estimates identifies cost changes. Detailed estimation is more accurate but also more time-consuming, so the appropriate method depends on the project information available. Accurate estimation is key to successful cost planning and avoiding cost overruns.