Three quantities, three different questions
Pixel count tells you how many sample positions a raster image contains: width multiplied by height. Print dimensions depend on how densely those pixels are placed: width in inches equals pixel width divided by pixels per inch, with the same calculation for height. Uncompressed channel data adds a storage assumption: the number of pixels multiplied by the number of bytes per pixel.
This tool assumes each selected channel uses eight bits, or one byte. RGB has three channels and RGBA adds an alpha channel, so the same image has a larger raw channel-data estimate in RGBA. The estimate excludes metadata, row padding, color profiles, application objects, and any additional image copies in memory.
Work through the default image
For 2400 × 1600 pixels, multiply the dimensions to get 3,840,000 pixels. RGB needs 3,840,000 × 3 = 11,520,000 bytes under the tool’s assumptions. Divide by 1,048,576 to express that quantity in mebibytes: approximately 10.986328 MiB. A megabyte, MB, uses a different divisor of 1,000,000; the label matters.
At 300 PPI, the width is 2400 ÷ 300 = 8 inches and the height is 1600 ÷ 300 ≈ 5.333333 inches. Changing to RGBA affects the memory estimate but not the print size. Changing to 150 PPI affects the print size but not memory or pixel count. Try those changes one at a time.
Why this is not a file-size predictor
An encoded image file can be much smaller than its decoded pixel data. Compression depends on the file format, image content, quality settings, metadata, and encoder. A flat-color graphic can compress very differently from a detailed photograph at the same dimensions. We therefore do not estimate download size from pixel dimensions alone.
For a real website, inspect the actual exported file size and its displayed dimensions. Do not use the raw-memory number as a bandwidth or loading-time prediction. A browser may also use different internal formats and additional buffers, so this number is not its total memory footprint.
Pixels per inch is not printer dots per inch
PPI describes how image pixels map to physical length. Printer DPI describes a printer’s marking resolution; one image pixel may be represented by several printer dots. The calculator works with image PPI only and does not model printer hardware, paper, viewing distance, or perceived sharpness. The 300 PPI default is an example, not a promise of ideal print quality for every use.
Limits and related reading
The tool accepts positive whole-number dimensions and density within the displayed limits. It does not resize, upload, inspect, or convert an actual file. It also does not estimate vector-file size: vector graphics describe shapes and paths rather than a fixed grid of color samples. Read pixels vs. vector for that distinction and MDN’s image-format guide for format-specific context.