The arithmetic for a row
Total arrangement width equals the sum of the frame widths plus (n − 1) times the gap. Four 11x14 frames at 3-inch gaps: 44 inches of frame plus 9 inches of gap equals 53 inches. Three 8x10 frames at 4-inch gaps: 24 plus 8 equals 32 inches. The gap count is always one fewer than the frame count, which is exactly where mental arithmetic goes wrong.
To centre that 53-inch row on a 96-inch wall, the left margin is (96 − 53) ÷ 2, or 21.5 inches. The frame left edges then run 21.5, 35.5, 49.5 and 63.5 inches from the left wall edge, stepping 14 inches each time: 11 of frame plus 3 of gap. The final right edge lands at 74.5 inches, leaving the same 21.5 inches of wall on the right.
With mixed widths the step changes at every frame, so write the sequence out. An 11x14, a 16x20 and an 11x14 at 3-inch gaps total 38 inches of frame plus 6 of gap, or 44 inches. Centred on the same 96-inch wall the left margin is 26 inches, and the three left edges are 26, 40 and 59 inches.
Vertical spacing and stacked rows
Rows use the same formula on the other axis. Two rows of 10-inch tall frames with a 4-inch gap stack to 24 inches overall. Setting the arrangement centre at 57 inches from the floor puts the bounding box bottom at 45 inches: the lower row occupies 45 to 55, the gap runs 55 to 59, and the upper row occupies 59 to 69 inches above the floor.
In a grid, keep vertical and horizontal gaps equal. The eye reads a grid as a lattice and compares every gap against every other, so a half-inch difference between the two axes is visible immediately. In a salon arrangement they can differ, because there is less repetition to compare against and vertical gaps end up carrying more of the visual structure.
Gap by frame size
Scale the gap to the smallest frame in each pair, not the largest. Frames up to 8x10 sit well at 1.5 to 2 inches. Frames from 11x14 to 16x20 usually want 2.5 to 3 inches. Pieces of 20x24 and up will take 3 to 4 inches without the group falling apart. Below about 1.5 inches, mouldings and mats start to collide visually; beyond about 5 inches, a group stops reading as one object.
Frame depth pushes the same numbers around. A deep or ornate moulding casts a shadow into the gap and makes it look narrower than it measures, so heavy mouldings want the upper end of each range. Thin metal frames can hold the lower end. Measure the gap between the outer edges of the mouldings, which is the edge the eye follows, not between the mats or the prints.
Consistent gaps versus optical gaps
A single fixed gap is the safe default and it is what a grid requires: six identical frames at slightly unequal gaps look like a failure rather than a decision. Set one number, apply it everywhere, and use distribute to enforce it rather than dragging by eye. Distribute divides the space between the first and last frame evenly across every frame in between.
Optical gaps are the exception, and they exist because the gap you measure and the gap you see are not the same. A wide mat, a pale image or a broad moulding pushes the visible edge of the picture inwards, so a 3-inch measured gap next to a heavily matted print can read as four. In a mixed arrangement, tighten measured gaps around visually heavy frames by about a quarter of an inch and check it on paper before committing.
Spacing around a mirror, a television or a window
A mirror or a television is not a member of the arrangement; it is the thing the arrangement defers to. Give it a larger gap than the frames give each other, with a floor of 4 to 6 inches measured from the outer bezel, mount plate or mirror edge, whichever projects further. That reads as deliberate separation rather than a failed attempt at alignment.
Add the screen, mirror or window as an obstacle rectangle before you lay out. Fit checks then treat it as a keep-clear zone and flag any frame that crosses it, and constrained auto-fit places the movable frames around it. For a window, measure to the outside of the architrave rather than to the glass, and keep frames clear of the sweep of any casement that opens inwards.
Spacing to the furniture and to the wall edges
Above a sofa or a console, size to the furniture rather than to the wall. An arrangement around two-thirds of the furniture width, centred on the furniture rather than on the wall, is the usual starting point. On an 84-inch sofa that is about 56 inches of arrangement, which four 11x14 frames at 3-inch gaps meet at 53 inches almost exactly.
Leave 6 to 10 inches between the top of the furniture and the bottom edge of the lowest frame. Closer and the group looks stuck to the sofa; further and the two stop reading as related at all. At the wall edges, keep more clear wall than your largest internal gap, because a frame sitting 3 inches from a corner looks like it slipped rather than like it was placed.
How the planner decides which frames are neighbours
Not every pair of frames has a gap worth reporting. A horizontal gap is measured only between frames whose vertical projections overlap by at least 45% of the shorter frame height. A 10-inch tall frame beside a 20-inch one needs at least 4.5 inches of shared vertical range before the space between them counts as a gap rather than as unrelated wall.
The Anchor balance template shows why this matters. Its lower 11x14 clears the 16x20 anchor by just one inch horizontally, but their vertical ranges overlap by only one inch against a 14-inch frame, far below the threshold. No gap is reported, because those two frames are not neighbours in any way a viewer perceives. The same test runs on the other axis for vertical gaps, using 45% of the narrower frame width.
One thing is never smoothed over. If two frames actually intersect, that is not reported as a zero gap; it is raised as a collision with both frames named. Overlap is a geometric error rather than a tight spacing choice, and it stays visible until you fix it.