---
epic: 2
story: 2.4
title: "Data Units (Binary vs Decimal)"
status: draft
---

## Epic 2 — Unit Conversion System
**Goal:** Support 200+ units across all major categories with SI prefix support.

### Story 2.4: Data Units (Binary vs Decimal)

As a CalcPad user working with digital storage,
I want correct differentiation between binary (KiB, MiB, GiB) and decimal (kB, MB, GB) data units,
So that my data size calculations match industry standards.

**Acceptance Criteria:**

**Given** the expression `1 MB in KB`
**When** the engine evaluates it
**Then** the result is `1000 KB` (decimal: 1 MB = 1000 KB)

**Given** the expression `1 MiB in KiB`
**When** the engine evaluates it
**Then** the result is `1024 KiB` (binary: 1 MiB = 1024 KiB)

**Given** the expression `1 GB in MB`
**When** the engine evaluates it
**Then** the result is `1000 MB`

**Given** the expression `1 GiB in MiB`
**When** the engine evaluates it
**Then** the result is `1024 MiB`

**Given** the expression `1 byte in bits`
**When** the engine evaluates it
**Then** the result is `8 bits`

**Given** the expression `1 MB in Mb` (megabytes to megabits)
**When** the engine evaluates it
**Then** the result is `8 Mb`
**And** case sensitivity distinguishes bytes (B) from bits (b)

**Given** the expression `5 GiB in GB`
**When** the engine evaluates it
**Then** the result correctly cross-converts: `5 * 1024^3 / 1000^3 = 5.36870912 GB`