Matting
Bottom-Weighted Mat Calculator
This bottom-weighted mat calculator sizes a mat with the bottom border set deeper than the top and sides, so your artwork sits at the optical center instead of looking like it sinks. It opens with bottom-weighting switched on — enter your artwork size, set how much extra to add, and copy the exact mat opening, outside and frame dimensions in inches or centimeters.
FramingMath · framingmath.com
Standard range ⅛–¼″ — enough lip to hold the art without hiding it.
Added to the bottom only. Typical ¼–1″.
Per side. Standard ¼″ (6 mm); typical ⅛–½″.
Optional — your photo stays on your device and is never uploaded. It’s cropped to fill the opening.
- Mat opening
- 7 1/2″ × 9 1/2″ approximately 19.1 × 24.1 cm
- Mat outside
- 11 1/2″ × 14″ approximately 29.2 × 35.6 cm
- Borders (T / B / L / R)
- 2″ / 2 1/2″ / 2″ / 2″ approximately 5.1 cm / 6.3 cm / 5.1 cm / 5.1 cm
- Glass / backing cut
- 11 3/8″ × 13 7/8″ approximately 28.9 × 35.2 cm
Rounded to the nearest 1⁄16″ (1 mm). The converted second unit, and any per-side or divided figure, may differ by up to that much. Showing exact decimals (to 0.001″ / 0.01 cm). The converted second unit, and any per-side or divided figure, may still differ in the last place.
How the bottom-weighted mat calculator works
The eye reads the middle of a frame as slightly above the true center. Give a mat equal borders all round and the picture can look like it is sitting low, so framers deepen the bottom border to push the image back up to where you expect it. If you want the full reasoning — optical versus geometric center — the bottom-weighting guide walks through it; this page is for getting the number and moving on.
There are two honest ways to set the extra, and the tool offers only these two. Fixed adds a set amount to the bottom alone: bottom = side + extra, so a 2″ side with a ½″ extra gives a 2½″ bottom and grows only the height. Proportional makes the bottom a percentage deeper than the sides: bottom = side × (1 + percent), so 20% deeper — the default — turns a 2″ side into a 2.4″ bottom. The top and sides never move in either mode, and the opening, outside and frame sizes update as you change the amount.
Worked example: an 11 × 14 portrait print
Take an 11 × 14″ print in portrait orientation. With a ¼″ overlap the window comes out 10½ × 13½″. Keep the top and sides at 2½″, then add ¾″ to the bottom, so the bottom border is 3¼″. The width is untouched at 15½″, but the height grows to 19¼″ — the mat outside, and the frame you order, is 15½ × 19¼″. Even borders would have given 15½ × 18½″; the whole ¾″ lives under the image, where it does its work.
Prefer to scale rather than add a flat amount? A portrait often takes about 30% deeper. Switch to Proportional, type 30, and the bottom lands on the same 3¼″ (2½ × 1.3 = 3.25″) — the two routes meet. The glass and backing drop in about ⅛″ smaller, near 15⅜ × 19⅛″. Use Copy or Share to grab the numbers, check a print-and-frame pairing with will it fit, or size the glazing on its own with the glass size calculator.
How deep should the bottom border be? Portrait vs landscape
How much to add is mostly taste, but orientation is a useful guide. A rough convention among framers: landscapes carry about 20% extra and portraits about 30–33%, because a tall frame shows the sinking effect more than a wide one. In Proportional mode those map straight onto the percentage field — 20 is the default, 30 suits most portraits. Treat them as starting points to judge by eye, not rules the calculator enforces: it computes exactly the Fixed amount or percentage you set, nothing hidden. If you like classical ratios, some framers relate the bottom to the top by the golden ratio, about 1.618 — the FAQ shows how to set that here. For a size-by-size table, the bottom-weighting guide lays it out.
Getting the most from the calculator
- Order the weighted outside, not the even one. The size to buy the frame and cut glass to is the taller Mat outside shown with weighting on — 15½ × 19¼″ in the example, not the even-border 15½ × 18½″. Miss it and the frame comes back short.
- Fixed for a clean cut, Proportional to scale. Fixed gives you a round fraction to cut or order to; Proportional keeps the ratio when you change the base border. Switching between the two never touches the width.
- Turn it off when the piece hangs low. For art above a sofa or on a shelf, the optical trick can reverse — set Bottom weight to None for even borders. Copy or Share saves the exact numbers to send to a framer.
Frequently asked questions
Should the bottom mat border be wider than the top?
For most art hung at or above eye level, yes. An even mat can make a picture read as sinking, so framers widen the bottom border to lift it to the optical center. This calculator opens with that weighting on — leave it on Fixed and the bottom grows while the top and sides stay put.
How much should you bottom-weight a mat?
Half an inch to one inch of extra suits most work: a quarter to a half on small prints, up to an inch on large ones. Type your amount into the Extra bottom border field and the outside height updates live. Our bottom-weighting guide has a finer, size-by-size table.
What percentage should the bottom be — landscape versus portrait?
As a rough editorial rule, landscapes take about 20% extra and portraits about 30 to 33%, since a taller frame shows the sinking effect more. In Proportional mode, 20% is the built-in default; type 30 for a portrait. Treat these as guides to eyeball, not fixed rules.
Is half an inch enough to bottom-weight a mat?
Usually, yes. Half an inch is the starting amount here and reads as balanced on prints up to about 16 by 20 inches. Larger pieces can carry three-quarters to a full inch without looking heavy; very small photos often need only a quarter. Adjust the field and judge by eye.
When should you not bottom-weight a mat?
Skip it, or use only a token quarter inch, for pieces that hang low or sit on a shelf, where the viewing angle reverses the effect, and for very small art where the extra barely shows. Set Bottom weight to None and the calculator returns to even borders on all four sides.
What is the golden-ratio mat method?
It is an editorial idea where the bottom border relates to the top by roughly 1.618, the golden ratio, for a classical feel. This tool has Fixed and Proportional modes, not a golden-ratio mode, so to approximate it you set the borders yourself — say a 2-inch top with a 3¼-inch bottom (2 × 1.618 ≈ 3.24).