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Megabit and ROM size converter
The cartridge said 16 MEG, but how many megabytes was that? Eight times less than it seemed: a megabit is not a megabyte. Convert between Kbit, Mbit, KB and MB using the binary convention cartridges followed, and discover the true size of the classics.
Famous cartridges: advertised megabits, real bytes
| Game | Advertised | Real size | Note |
|---|---|---|---|
| Super Mario Bros. (NES, 1985) | 0.3125 Mbit | 40 KB | 40 KB: 32 KB program + 8 KB graphics |
| The Legend of Zelda (NES, 1986) | 1 Mbit | 128 KB | Nintendo's first battery save cartridge |
| Super Mario World (SNES, 1990) | 4 Mbit | 512 KB | the famous 4 Mega cartridge |
| Sonic the Hedgehog (Mega Drive, 1991) | 4 Mbit | 512 KB | same size as its rival |
| Street Fighter II (SNES, 1992) | 16 Mbit | 2 MB | the box shouted 16 MEG |
| Donkey Kong Country (SNES, 1994) | 32 Mbit | 4 MB | pre-rendered graphics need room |
| Tales of Phantasia (Super Famicom, 1995) | 48 Mbit | 6 MB | with Star Ocean, the biggest SNES cartridge |
| Super Mario 64 (N64, 1996) | 64 Mbit | 8 MB | an entire 3D world in 8 MB |
| Zelda: Ocarina of Time (N64, 1998) | 256 Mbit | 32 MB | 32 MB, 64 times Super Mario World |
| Conker's Bad Fur Day (N64, 2001) | 512 Mbit | 64 MB | 64 MB, the ceiling of commercial N64 carts |
The historical megabit confusion
In the 90s, Super Nintendo and Mega Drive boxes shouted 4 MEG, 8 MEG, 16 MEG, and an entire generation grew up thinking those were megabytes. They were megabits. Since ROM chips were sold by capacity in bits, marketing inherited the factory unit, and the difference is a factor of 8: Super Mario World's famous 4 Meg cartridge holds a mere 512 KB, half a 3.5 inch floppy. The largest commercial SNES cartridge, a title shared by Tales of Phantasia and Star Ocean, held 48 Mbit: 6 MB.
The math is direct and binary, as befits cartridges: 1 Mbit = 1,024 Kbit = 131,072 bytes = 128 KB, and 8 Mbit = 1 MB. The same convention covers saves: the battery backed SRAM in SNES cartridges typically shipped with 16 to 64 Kbit, that is, 2 to 8 KB, enough for three adventure slots and nothing more. That is why games of the era saved so little: every save byte cost battery and silicon.
The unit's death blow came with the CD: when the PlayStation arrived carrying 650 MB per disc, advertising 64 megabits (8 MB) became embarrassing, and the industry switched to megabytes for good. What remains is a trap for collectors: when an old ad says meg, it almost always means megabit, and the table below translates the celebrated cases.
Sources: ROM sizes checked against SNES Central entries, Fabien Sanglard's article Inside the Super Nintendo cartridges, and the preservation community's verified dump databases.
More CRT era tools: integer scaling calculator, 4:3 aspect ratio correction, ms to frames lag converter and console resolution archive. And if nostalgia strikes on another frequency, every pixel on these consoles was addressed in binary.
Last updated: · Methodology and sources