Formula and method
Columns = ceil(length ÷ your maximum spacing). Rows = ceil(width ÷ your maximum spacing). Actual spacing is room dimension ÷ cell count. Each fixture center is half a cell from its nearest wall.
Worked example
For a 16 ft × 12 ft room and your chosen 4 ft maximum spacing: 4 columns × 3 rows = 12 proposed positions. Actual spacing is 4 ft in both directions; wall offsets are 2 ft.
Assumptions
The preview is a geometric grid only. It assumes a simple rectangle and an unobstructed ceiling. You supply the maximum spacing; no ceiling-height rule or fixture performance is inferred.
Important limitations
Not a photometric calculation, illumination guarantee, electrical design, wiring check, or code/safety approval. Fixture output, beam angle, reflectance, mounting height, tasks, cabinetry, furniture, and obstructions may require a different layout.
Frequently asked questions
Does the grid tell me how many lights are required? No. It shows the count implied by your entered maximum spacing. Are wall offsets fixed? No, they are half the actual equal-cell spacing in each direction.
Privacy
Your inputs and result stay in this browser tab. This calculator does not send entered values to a server, save them in browser storage, or put them in the URL.