A picture frame calculator should do more than add two mat borders to a print. Custom framing is a stack of related rectangles: the artwork, the mat window, the glass, the rabbet, and the moulding face. If any one of those is guessed, the frame either looks cheap or the package will not fit. This calculator keeps every step in millimetres internally, then formats the answer in inches, centimetres, or millimetres so a hobby framer and a small shop can share the same numbers.
Start with the artwork. Photographers often talk in 8×10, 11×14, and 16×20. Print labs sometimes deliver slightly oversized paper. Fine-art inkjet sheets can be 13×19 or 17×22. Whatever you have, measure the image you want to keep, not the spare paper around it. The mat overlap — usually 1/8" to 1/4" — hides the raw edge and stops a sliver of white from flashing around the window. This tool subtracts overlap from the artwork to produce the true mat window, then adds your chosen borders to produce the package that glass and backing must match.
Bottom weighting is not decoration. A mat that is equal on all four sides can look top-heavy once the frame is on the wall, especially on portrait prints. Many framers add 1/2" or 1" extra at the bottom. The calculator lets you set a wider bottom without forcing the other three sides to follow. If you later open Framing Studio, those same borders become draggable edges with smart snap to 2", 2.5", and 3" plus a Symmetric / Bottom weighted hint.
The finished outside size is not the glass size. Moulding has a face width and a rabbet lip. The lip covers the glass; the face is what you see from the room. Fitting clearance gives the package a little room to drop into the rabbet so humidity and slightly proud corners do not jam the stack. The engine uses: rabbet = package + 2×clearance; sight = rabbet − 2×lip; outside = sight + 2×face. That is the same geometry used for long-point rail lengths in the workshop.
DIY picture framing usually fails at the last 3 mm. A mitre that is theoretically the glass size will be short once you account for face width. A mat cut to the print size with no overlap will creep. A double mat with no reveal looks like a thick single mat. This page exists so searchers who typed “picture frame calculator” can get a trustworthy first answer in seconds, then graduate to the visual studio instead of bouncing to a spreadsheet.
Etsy sellers and edition printers can run several sizes in one sitting. An 8×10 with a 2" mat is a different SKU from an 11×14 with a 2.5"/3" weighted mat, even if both hang in the same collection. Because the math is a single FramePlan, the workshop later can batch rails across a whole project and pack them onto 96" sticks. The calculator is the acquisition layer; the studio is where you stay.
Units are a common source of silent error. Inches in sixteenths, centimetres from a European print, millimetres from a CNC mat cutter — they all convert to canonical millimetres here. Display uses inch fractions when you work in inches, so 2 1/2" stays 2 1/2" instead of 2.499. If you export SVG from the studio, the millimetre viewBox matches this calculator, which is useful for a paper template even though we do not market those files as CNC-ready.
Use the result as a sanity check against ready-made frames. If your package lands 1/4" away from 16×20, the studio will offer a snap to that standard size. Keeping custom is always allowed. Ready-made frames are sold by the opening they accept, which is why this calculator reports package/glass size beside the outside dimension. Buy the frame for the package, cut moulding for the outside.
Nothing leaves your browser. There is no account and no image upload on this page. When you continue into the studio you can drop a JPG, PNG, or WebP locally; that file is read with FileReader and stored in IndexedDB on your machine. That matters for photographers who do not want unpublished work sitting on a random calculator server.
If you are framing a certificate, a poster, or a wedding print, run the calculator once, then open the studio to preview wall scale. A 24×36 poster in a 3" moulding is a piece of furniture. The wall view exists so you see that before you buy acrylic. The picture frame calculator is the fast door; the workshop optimizer is why the site is not just another form.
Frequently asked questions
Does this picture frame calculator include the moulding width?
Yes. Face width and rabbet overlap are part of the finished outside size, not just the mat borders.
Should I measure the print or the visible image?
Measure the image you want to keep. Mat overlap then hides the edge inside the window.
Why is the outside size larger than glass size?
The moulding face sits outside the sight opening. Glass matches the package, not the outer edge of the frame.
Can I use centimetres?
Switch the unit control. Internally everything is millimetres, so inch and metric jobs share one engine.