There is no single method that all roofers use to measure a roof. The approach depends on roof design, safety considerations, and the level of accuracy needed for the project.
On-site measuring involves physically measuring roof planes, edges, and slopes, or taking ground measurements that are adjusted for pitch. This method allows contractors to see roof condition, access points, and details that affect labor and materials. It can be more time-intensive, but it provides firsthand context.
Aerial measurements use overhead imagery to estimate roof dimensions remotely. These measurements are faster and can be useful for early planning or comparison. However, they may miss subtle changes in slope or areas hidden from view.
Many careful contractors use both methods. Aerial data provides a starting point, while on-site checks confirm critical dimensions and roof complexity. This combined approach helps reduce surprises later in the project.