Aspect Ratio Calculator for Art – Scale, Crop and Grid Any Picture

Our free aspect ratio calculator is made for artists. It finds the ratio of any picture, canvas, or sheet of paper, works out a missing side, and enlarges or reduces a drawing without distortion. It also shows you exactly what gets cropped when your photo goes onto a canvas with a different shape, and it calculates the grid for the grid method on both the reference and the canvas. Inches, centimeters, millimeters, and pixels all work, and everything runs in your browser.

How to Use the Aspect Ratio Calculator

The calculator has six tabs, one for each question that comes up when you plan a drawing or a painting.

1. Aspect ratio. Enter the width and height of a picture, a canvas, or a sheet of paper. You get the exact ratio (for example 4:5), the decimal form, the nearest standard ratio with its deviation, and a list of standard formats that share the same ratio.
2. Missing side. Pick a ratio such as 3:4 or 16:9, or type your own, then enter the width or the height. The other side appears at once, together with the formula.
3. Scale. Enlarge or reduce a picture by percent, by a factor, to a new width, to a new height, or so that it fits inside a box. The quick picks include the copier settings 71% and 141% for going between A4 and A3.
4. Fit on canvas. Enter the size of your picture and choose a canvas, a paper size, or a photo print size from the list. The preview shows what you lose with “Fill and crop” or how wide the empty border gets with “Fit with border”.
5. Grid method. Enter the size of your reference and of your drawing surface, then the number of squares. You get the square size on both sides and a table with the position of every grid line.
6. Compare. Lay common ratios on top of each other at the same height, width, or area to see how much they really differ.

You can type decimals with a point or a comma and fractions like 8 1/2. “Use a photo” reads the pixel size of an image on your device, and the photo then appears in the preview. “Print or save PDF” prints the current result on US Letter or A4, and “Copy share link” saves all your values in a link.

What Is an Aspect Ratio?

The aspect ratio is the relationship between the width and the height of a rectangle. It is written as two numbers with a colon, width first. A canvas of 16 × 20 inches has a ratio of 4:5, because both sides can be divided by 4. The ratio says nothing about the size. An 8 × 10 in sketch, a 16 × 20 in canvas, and a 40 × 50 cm stretched canvas all have the same 4:5 shape, so a composition drawn on one fits the others without cropping.

Ratio is closely linked to proportion in art. If you change the width without changing the height by the same factor, every shape gets stretched.

How to Calculate an Aspect Ratio

Divide the width and the height by their greatest common divisor. For 1,920 × 1,080 pixels, the greatest common divisor is 120, which gives 16:9. For sizes with decimals, first multiply both sides by 10 or 100. US Letter, 8.5 × 11 in, becomes 85 × 110 and then 17:22. If you divide the width by the height, you get the decimal form instead: 16:9 is 1.778:1, and a portrait 4:5 is 1:1.25.

Exact Ratio, Simple Ratio, and Nearest Standard

Many real formats do not reduce to small numbers. A4 paper is 210 × 297 mm, which is exactly 70:99. That is why the calculator shows three answers. The exact ratio is mathematically correct. The simple ratio is the closest ratio with small numbers, 5:7 for A4, with a deviation of about 1%. The nearest standard tells you which familiar format the shape belongs to. For A4, that is 1:√2, the ratio of all ISO A sizes.

Common Aspect Ratios in Art

These ratios cover almost every canvas, paper, and photo size you will meet in an art store.

The 4:5 and 3:4 families explain why so many standard canvas sizes look alike. If you want a format with classical harmony, the golden rectangle is a popular choice, and our article on the golden ratio in art explains where it comes from.

How to Enlarge a Drawing Proportionally

To keep the proportions, multiply both sides by the same factor. The factor is the new size divided by the old size. If you want to enlarge an 8 × 10 in drawing to a width of 16 in, the factor is 16 ÷ 8 = 2, so the new height is 10 × 2 = 20 in. In the “Scale” tab, choose “Width”, type 16, and the calculator does the rest.

Percent, Factor, and Fit in Box

A factor of 2 is the same as 200%, and a factor of 0.5 is 50%. On a copier, A4 to A3 is 141%, because the A sizes grow by √2 from one size to the next. “Fit in box” is the right choice if the picture must stay inside a certain space, such as a 50 × 40 in wall area. The calculator uses the smaller of the two factors, so the picture touches the box on one side and stays within it on the other.

Why the Area Grows Faster Than the Sides

When you double the width and the height, the area becomes four times as large. A painting at 200% needs about four times as much paint, gesso, and time to cover, and a mural at 500% has twenty-five times the area of the sketch. The calculator shows this area factor next to every result, which helps when you plan materials for a large piece such as a mural.

Will Your Picture Fit the Canvas?

Most reference photos have a ratio of 2:3 or 3:4, while many canvases are 4:5. If the ratios differ, you have two options, and the “Fit on canvas” tab shows both.

• Fill and crop. The picture is scaled until it covers the whole canvas, and the parts that stick out are cut off. A 4 × 6 in photo on a 16 × 20 in canvas is enlarged to 16 × 24 in, so 2 in are lost at the top and at the bottom. On the photo itself, that is 0.5 in per side, and 16.7% of the picture is gone.
• Fit with border. The picture is scaled until it touches the canvas on two sides, and the rest stays empty. The same photo becomes 13.33 × 20 in and leaves a 1.33 in strip on the left and the right. You can paint that strip as background or plan the composition around it.

The table under the result lists the best-fitting standard formats for your picture. For a 4 × 6 in photo, 12 × 18 in, 20 × 30 in, and 24 × 36 in canvases fit without any crop, as do 20 × 30 cm and 30 × 45 cm. Click “Use” to try one of them. It also shows the canvas size that would match your picture exactly.

If your picture is a digital file, choose pixels as the unit. The calculator then shows the print resolution on that canvas. At 300 dpi, a print looks sharp even up close. For canvas prints that are viewed from a distance, 150 dpi is usually enough. If you plan to frame the result, our picture frame size calculator works out the mat and the frame.

Scaling Up With the Grid Method

The grid method is the classic way to transfer a small reference to a large surface by hand. You draw a grid of squares over the reference and a grid with the same number of larger squares on the canvas, then copy one square at a time. It is still the most reliable way to enlarge a drawing without a projector. Our guide to drawing with a grid covers the technique in detail.

How to Calculate the Grid

Both grids need the same number of squares. The square size on the canvas is the square size on the reference times the scale factor. Here is how the calculator works it out for a 4 × 6 in reference on a 16 × 20 in canvas with 6 squares across:

1. The reference is scaled to fit the canvas. The width allows a factor of 4, the height only 3.33, so the factor is 3.33 and the drawing area is 13.33 × 20 in.
2. Six squares across a 4 in reference make 0.67 in squares. On the canvas, they become 0.67 × 3.33 = 2.22 in, a little more than 2 1/4 in.
3. The reference is 6 in tall, so you need 9 rows. The grid has 6 × 9 = 54 squares.
4. The drawing area is 2.67 in narrower than the canvas, which leaves a 1.33 in margin on each side.

The table “Where to draw the grid lines” lists every line position from the left and top edge, with the margin already included. You can measure them off with a ruler and do not need to add anything up. If you prefer a fixed square size, such as 1 in on the reference or 5 cm on the canvas, set “Set the grid by” to “Reference” or “Drawing”.

Putting the Grid on Your Reference

For the reference, you can print it with the grid. Load your photo in the “Grid method” tab and choose “Print or save PDF”, and the second page shows your photo with the grid and the letters and numbers for each square. Our Art Grid Tool also puts a grid over any photo. Set it to the same number of squares across as in the calculator. On the canvas, draw the grid lightly with a hard pencil (2H) or with a water-soluble pencil, so it disappears under the paint or can be erased.

Tips for Scaling Art Without Mistakes

• Measure the real reference. Use the size of the printed photo or the sketch you are copying from, not the size you think it has. A 10 × 15 cm print is not the same as a 4 × 6 in print.
• Plan the crop before you start. Decide which part of the reference matters most. In “Fill and crop”, the cut is split evenly between both edges, so mark the center on your reference.
• Keep the drawing light. Grid lines and transfer lines should be easy to remove. If you trace parts of the image instead, our article on tracing pictures compares the methods.

Your Photos Stay Private

The calculator runs entirely in your browser. A photo you load is read on your device and never uploaded, and the share link only contains your numbers.

More Free Art Tools

All our tools are free, run in your browser, and need no account. See them all on the free art tools page.

• Photo to painting: turn a photo into an oil or watercolor painting.
• Photo to sketch: turn a photo into a pencil sketch or line art.
• Photo to coloring page: turn any picture into a printable coloring page.
• Image to pixel art: convert an image into editable pixel art.
• Notan generator: plan light and dark shapes with a two- or three-value study.
• Art grid tool: put a drawing grid over any photo.
• Pose reference: practice figure drawing with timed poses.
• Graph Paper Printable: print graph paper, dot grid, isometric, and hex paper to scale.
• Online drawing board: draw and paint online with brushes, layers, and symmetry.
• Golden ratio overlay: check your composition with a golden spiral and rule of thirds.
• Perspective grid generator: print one-, two-, and three-point perspective grids.
• Paint by number generator: turn a photo into a printable paint by number template.
• Mandala maker: draw symmetrical mandalas and print them as coloring pages.
• Connect the dots maker: turn a picture into a printable dot to dot worksheet.
• Picture frame and mat size calculator: work out mat openings and frame sizes for your art.
• Image color picker: find the exact colors in any photo or painting.
• Color name finder: get the name of any HEX, RGB, or photo color.
• Color wheel: find complementary, triadic, and analogous colors.
• Color mixer: mix paint or screen colors and find paint recipes.
• Color palette generator: create matching color schemes or a palette from an image.
• Random color generator: get random colors and palettes with paint mixing tips.
• Tint and shade generator: make tints, shades, and tones of any color.
• Color blindness simulator: see images and palettes as color blind people do.
• Art pricing calculator: find a fair price for your paintings and prints.
• Art quiz: guess famous paintings, artists, and styles.
• Art prompt generator: get random ideas for drawing and painting.
• Random character generator: create an original character with traits and a palette.

Frequently Asked Questions

How Do I Calculate the Aspect Ratio of a Picture?

Divide the width and the height by their greatest common divisor. A 16 × 20 in canvas has a ratio of 4:5, and a 1,920 × 1,080 pixel image has a ratio of 16:9. For the decimal form, divide the width by the height. The calculator above does both and also finds the nearest standard ratio.

How Do I Enlarge a Drawing Without Distorting It?

Multiply the width and the height by the same factor. To go from 8 × 10 in to a width of 16 in, the factor is 2, so the height becomes 20 in. For enlarging by hand, the grid method transfers the drawing square by square.

What Size Squares Should I Use for the Grid Method?

On the reference, squares of 1/2 to 1 in (1 to 2.5 cm) work well. Smaller squares give more accuracy in detailed areas like faces, but they take longer. The square on the canvas is the reference square times the scale factor, so a 1 in square at 300% becomes 3 in.

What Is the Aspect Ratio of A4 Paper?

A4 measures 210 × 297 mm, which is 1:1.414, or 1:√2. All A sizes share this ratio, so A4 enlarged by 141% gives A3. As a simple ratio, A4 is close to 5:7.

Can I Use Pixels in the Aspect Ratio Calculator?

Yes. Choose “px” as the unit. In the “Fit on canvas” tab, the calculator also shows the resulting print resolution in dpi and the largest size the image prints sharply at 300 dpi.