Name the body side and surface: left outer forearm is more useful than arm. Give a rough longest dimension and width, or say how much of the area the tattoo should cover. A clear placement photo can show curvature, existing work, and where the composition should begin and end. If you are considering that area, the forearm tattoo guide shows eight reviewed placements and the exact planning inputs. If the idea may grow across most of the arm, the sleeve and half-sleeve planning guide covers hierarchy, transitions, stopping points, and full-arm photographs. For visible hand or finger work, the hand and finger tattoo guide separates the exact surface, work constraints, longevity uncertainty, and seven reviewed examples.
Centimetres do not calculate hours. Subject, style, detail, placement, body position, design changes, setup, and breaks also affect the session structure. The size and session guide explains the five useful inputs and preserves the boundary between Alex's published rates and your eventual estimate.