Six free calculators, each answering one question a painting business has to get right to make money. No account, no card, and every one of them uses the same production-rate model that prices jobs in Surfacely.
Most painting estimates are built from a price per square metre carried in someone's head. These tools work the way a costed estimate does: measure the surface, apply a production rate for how fast that surface is painted, add prep as its own rate, then apply a margin to the cost.
That is why a narrow trim profile and a broad wall of the same area do not cost the same, and why prep on a weathered exterior is charged as hours rather than as a percentage uplift.