WORK WITH THE FRAME YOU ALREADY HAVE
Find the mat borders.
Compare your frames.
Enter the artwork and the actual mat outside dimensions. Compare up to three single-window mats with the same overlap and minimum border.
Examples are synthetic. Start your comparison before entering real measurements. Nothing is uploaded.
Measure the mat, not the frame outline
Artwork: the whole photo or print. Window: the visible rectangle after your chosen overlaps. Mat outside: the board’s outside edges that fit your existing frame. Frame outside: the decorative outline; it is not the mat size.
Original schematic, not a cutting-scale drawing. If the mat is missing, measure the actual backing/glazing size that fits and verify it at the frame’s back rabbet. Frame package labels may use another reference. Existing pre-cut window sizes are not mat outside dimensions.
02 / SAME CONDITIONS, SIDE BY SIDE
Your mat candidates
Enter each mat’s actual outside width and height. Labels such as “11 × 14 frame” do not prove that measurement. The tool checks geometric borders; all frame assembly conditions remain unknown.
Take a selected mat to the workshop
Export a parameter card directly, without stock, rates or saw inputs. To use the bench’s work-card workflow, confirm the mat measurement and choose Stage for work card. Then restore the intended workshop job and click Review selected mat there. You review the geometry before applying it; inventory, rates, kerf, job reference and notes are preserved. No automatic job save.
Open workshop planner to review ↗The two pages use the same origin’s local browser storage for staged geometry. Switching browsers or addresses does not transfer it. Example geometry can only be applied to an example workshop job. Your comparisons and exports never go into a URL or network request.
How the existing-frame mat calculator works
- Measure artwork outside width and height, then choose the amount each mat edge covers.
- Measure the mat outside edges for each existing frame. Do not enter the decorative frame outline.
- Choose centred borders or the explicit difference between bottom and top. Set your own minimum, or leave it unknown.
- Compare border widths, highlighted shortfalls and measurement confirmation. Export the candidate’s card; check frame fitting before ordering or cutting.
The formulas
Window width = artwork width − left overlap − right overlap. Window height = artwork height − top overlap − bottom overlap.
Left = right = (mat outside width − window width) ÷ 2. If bottom extra is d: top = (mat outside height − window height − d) ÷ 2; bottom = top + d. The outside board never grows when you add bottom weight. At integer micrometre precision, a one-micrometre remainder goes right/bottom.
A hand-checkable 8 × 10 → 11 × 14 example
With 1/8 in covered on each edge, the window is 7 3/4 × 9 3/4 in. An 11 × 14 in mat leaves 1 5/8 in left/right and 2 1/8 in top/bottom. Asking for the bottom to be 1/2 in wider gives 1 7/8 in top and 2 3/8 in bottom. The mat stays 11 × 14 in.
When a candidate is not usable
An opening wider or taller than the mat cannot leave borders. Overlaps that consume the artwork block every candidate. A border under your minimum is marked by edge and shortfall, not silently accepted. A geometrically valid mat still needs a real fit: lip cover can reduce its visible border, the stack may exceed rabbet depth, and mounting suitability is not known from these dimensions.
This page covers one rectangular window in one mat. It does not crop or upload artwork, certify conservation framing, calculate double mats or machine blade positions. Front previews are illustrative and not at cutting scale.
Sources & scope of the evidence
Logan’s free border calculator distinguishes the frame’s back/rabbet size from its outer outline and supports offsets and layers. Metroframe’s mat calculator already derives borders from inner/outer sizes, including weighted bottoms. This page adds a bounded comparison of three user-measured candidates; centring and weighted borders are established methods.
A public framing question illustrates confusion about an existing mat and artwork overlap. It is one anecdote, not demand volume or conservation advice. Sources checked 12 October 2026. The formulas, schematic and examples here are original explanations. Search traffic, demand for comparison and superiority to other tools remain unmeasured.