File Size Unit Conversion Table

SI units (decimal) versus IEC units (binary)

File sizes are expressed with two different families of units: decimal units from the International System of Units (SI), and binary units defined by the IEC. Confusing MB with MiB is a common reason boundary tests fail.

MB to bytes conversion table

How major services and tools interpret these units

Formula

// Conversion helpers in JavaScript
const UNITS = {
    // SI（10進数）
    KB: 1_000,
    MB: 1_000_000,
    GB: 1_000_000_000,
    TB: 1_000_000_000_000,
    // IEC（2進数）
    KiB: 1_024,
    MiB: 1_048_576,
    GiB: 1_073_741_824,
    TiB: 1_099_511_627_776,
};

const toBytes = (value, unit) => value * UNITS[unit];
const fromBytes = (bytes, unit) => bytes / UNITS[unit];

// Example: 10 MiB to bytes
console.log(toBytes(10, 'MiB')); // → 10485760

// Example: 10,000,000 bytes to MB
console.log(fromBytes(10_000_000, 'MB')); // → 10
console.log(fromBytes(10_000_000, 'MiB').toFixed(2)); // → 9.54

 1_000, 'MB' => 1_000_000, 'GB' => 1_000_000_000,
        'KiB' => 1_024, 'MiB' => 1_048_576, 'GiB' => 1_073_741_824,
    ];
    return (int)($value * ($units[$unit] ?? 1));
}

echo toBytes(10, 'MiB');  // → 10485760
echo toBytes(25, 'MB');   // → 25000000

Matching boundary-test files

DevLab provides boundary-test files sized to the common upload limits. Pick the one that matches how the target system interprets the unit.

• Threshold test files — sets of three files sized just under, exactly at, and just over each limit