Why 1/8 Inch Accuracy Changes Everything
A 1/4 inch error sounds small. But in picture framing, that gap shows. If one side of your mat opening is wider than the other, the artwork looks off-center. If the opening is too tight, the paper buckles. And because mat borders get added to all four sides, a small mistake in your starting numbers carries through the whole calculation.
Ready-made frames hide small errors because they only come in set sizes. Picture framing does not have that safety net. Every fraction of an inch matters, which is why we measure to the nearest 1/8 inch. The steps below show you how to measure prints, canvas, textiles, and 3D objects so your frame fits right the first time.
Step 1: Start with the Right Measuring Tools
Use a rigid metal ruler or a metal carpenter's square. Metal does not stretch, bend, or warp the way cloth tapes and plastic rulers do. A 24-inch or 36-inch metal ruler covers most artwork sizes. For pieces longer than your ruler, a locking carpenter's tape measure with clear 1/8-inch markings works well. Keep the tape straight and taut while measuring.
Avoid sewing tapes, wooden rulers, and flexible plastic rulers. These tools introduce small variations through stretching, warping, or inconsistent tension. For miniature artwork, digital calipers provide extreme accuracy, but they are not necessary for standard framing where 1/8-inch precision is the target.
Step 2: Record Width and Height at the Widest Points
Lay your artwork flat on a clean surface. Measure the width (left to right) and the height (top to bottom) at the widest points. Record both numbers to the nearest 1/8 inch. Do not round to the nearest half inch. Write down exactly what you measure, including fractions.
For Prints on Paper: Decide whether you want to show the paper margins or hide them under the mat. If you want to hide them, measure only the printed image area. Place the ruler at the edge of the printed image, not the paper edge. Most prints have 1 to 2 inch white borders that look cleaner tucked under a mat. If your print has a pencil signature or edition number in the margin, include that area in your measurement.
For Stretched Canvas: Measure the outer dimensions of the stretcher bars across the front face. Do not include the side depth. Canvas is usually framed without a mat, so the frame must match the canvas dimensions closely. Measure at two or three points along each side, since handmade stretchers can vary slightly. Use the largest number to make sure the canvas fits.
For Textiles and Fabrics: Secure the fabric to a rigid backing board first, then measure the backing. Loose fabric shifts during measurement and gives unreliable numbers. Decide whether the fabric edges will be visible or hidden under a mat before recording your final dimensions.
For Three-Dimensional or Irregular Objects: Measure the maximum width and maximum height to find the smallest rectangle that contains the entire object. Measure thickness separately. You will need this number to specify the frame depth, especially for shadowbox frames. Add at least 1/4 inch of clearance between the object and the glazing.
Step 3: Choose Your Mat Border Width
The mat border is the colored border between your artwork and the frame edge. Border width changes how the finished piece looks and how large the frame needs to be. A good starting point is one-third of your artwork's shortest side. This rule works well for most artwork sizes and keeps the math simple.
Small Artwork (under 11x14 inches): Use 2 to 2.5 inch borders. An 8x10 print divided by three gives roughly 2.67 inches. Most framers round to 2.5 or 3 inches. Very small pieces (5x7 and under) can handle slightly wider borders, up to half the shortest side, to keep the framed piece from looking too small on a wall.
Medium Artwork (11x14 to 18x24 inches): Use 2.5 to 3.5 inch borders. This range gives artwork enough space around it without making the frame too large. An 11x14 print with 3-inch borders, for example, makes a 17x20 inch frame. That is a good size for most walls.
Large Artwork (over 24x36 inches): Use 3.5 to 4 inch borders. The one-third rule creates borders that are too wide at this size. A 30x40 print at one-third would need 10-inch borders, making a 50x60 inch frame. Most framers keep large artwork borders between 4 and 6 inches. Some large pieces look better in floater frames with no mat at all.
Think About Viewing Distance: Artwork that people see from across the room (10+ feet away) looks better with wider borders. Pieces in hallways or small rooms (3 to 5 feet away) work well with narrower borders. Think about where the frame will hang before picking your border width.
Step 4: Calculate Your Frame Dimensions
Prefer to skip the math? You only need your artwork size. Our frame designer adds the mat borders and shows you the exact frame size and price. The steps below are here if you want to see how the math works or check a size by hand.
Add the mat border width to every side of your artwork size. This is where most ordering mistakes happen: adding the border to only one side instead of both. Width and height each need the border added twice, once for each side.
The Formula:
Frame Width = Artwork Width + (Mat Border x 2)
Frame Height = Artwork Height + (Mat Border x 2)
Example 1: Standard Print
Artwork: 16 x 20 inches
Mat Border: 3 inches on all sides
Frame Width: 16 + (3 x 2) = 22 inches
Frame Height: 20 + (3 x 2) = 26 inches
Frame Size: 22 x 26 inches
Example 2: Photo with a Weighted Bottom
Artwork: 11 x 14 inches
Top and Side Borders: 3 inches
Bottom Border: 3.5 inches
Frame Width: 11 + (3 x 2) = 17 inches
Frame Height: 14 + 3 (top) + 3.5 (bottom) = 20.5 inches
Frame Size: 17 x 20.5 inches
Example 3: Large Poster
Artwork: 24 x 36 inches
Mat Border: 4 inches on all sides
Frame Width: 24 + (4 x 2) = 32 inches
Frame Height: 36 + (4 x 2) = 44 inches
Frame Size: 32 x 44 inches
Double-check your math by working backward. Subtract the border widths from the frame size. If you get back to your original artwork size, the numbers are correct. If your bottom border is wider than the top, subtract the top and bottom values one at a time.
Or skip it entirely. Enter your artwork size in the frame designer and we will size the frame for you.
Step 5: Confirm Rabbet Depth and Mounting Clearance
The rabbet (say "rabbit") is the small shelf inside the frame that holds the glazing, mat, artwork, and backing in place. Standard rabbets are 3/8 to 1/2 inch deep. That is enough room for most flat artwork. When you order a custom frame, the maker sizes the rabbet for you based on the frame dimensions you enter.
Shadowbox frames and deep frames for 3D objects are different. For those, you need to tell us both the outer frame size and how much interior depth you need. Measure how thick your object is and add at least 1/4 inch so it does not press against the glazing.
How you mount the artwork can also affect fit. Hinge mounting needs a backing board slightly smaller than the frame opening to leave room for the hinge strips. Dry mounting uses a board cut to the exact opening size. If you are not sure which method to use, note your choice when ordering so the frame is sized to match.
Five Measurement Errors That Lead to Reorders
Measuring Paper Instead of Image Area: White margins around a print should be hidden under the mat. If you measure the full paper size instead of the printed image, the frame will be 1 to 2 inches too large. The mat opening will expose blank paper on all sides, and the framing will look unfinished.
Adding Mat Borders to One Side Only: This is the single most common calculation error. Mat borders surround the artwork on all four sides. That means you add the border width twice per dimension: left plus right for width, top plus bottom for height. Forgetting to double the border shortens the frame by the full border width on one axis.
Mixing Inches and Centimeters: All numbers must use the same unit. U.S. picture framing uses inches in 1/8-inch steps. If you measure in centimeters, convert to inches before ordering (1 inch = 2.54 cm). Even one mixed number throws the whole calculation off by an inch or more.
Rounding to the Nearest Half Inch: A 16.25 x 20.125 inch piece is not the same as 16 x 20 inches. That 1/4 inch difference gets carried through every border you add. The gaps show clearly once the artwork is in the frame. Write down exact numbers in 1/8-inch steps, even when the fractions seem small.
Preview and Verify with Digital Tools
Frame designers with built-in calculators do the math for you. Enter your artwork size, choose a mat border width, and the tool shows your frame size right away. It also shows a preview of how the finished piece will look before you place an order.
Use the preview to compare different border widths side by side. Try 2.5 inches, then 3 inches, then 3.5 inches. The difference is easy to see, and checking it on screen is more helpful than trying to picture it in your head. Some tools also show how mat color, frame moulding, and glazing (the clear cover over your artwork) look together.
For artwork you cannot replace, print a full-size template of your frame opening. Cut out the center and lay it over your artwork to test the border width in person. This removes all guesswork and confirms that your chosen layout looks right at actual size before any materials are cut.
Handling Difficult and Non-Standard Pieces
Warped or Buckled Artwork: Flatten the piece as much as possible before measuring. Place it under a sheet of glass or a stack of heavy books overnight. Measure the flattened dimensions, since the framing process will press the artwork flat against the backing. For severely warped pieces, consult a professional framer before ordering.
Torn or Ragged Edges: Measure to the farthest point of each edge in both directions. This gives you the largest rectangle the frame needs to cover. Uneven edges should be hidden under the mat with enough overlap to stay out of sight. Add your standard border widths to those maximum numbers.
Multi-Panel Artwork (Two or Three Pieces): Measure each panel on its own. Add the gap you want between panels (usually 1/4 to 1/2 inch) to the combined panel widths. Then add mat borders around the full group, not around each panel. This keeps everything in one clean frame.
Fragile or Delicate Materials: Do not press metal rulers against surfaces that scratch or dent easily. Use a clear acrylic ruler, or flip the piece over and measure from the back. For very delicate items, take a sharp photo next to a ruler and measure from the image on screen. This avoids repeated handling.