Real Disk Capacity Calculator

SSD and hard disk drives often don't meet the storage capacity claims of their manufacturers. Have you ever seen a USB hard drive advertised with 2 TB storage space, yet it only gives you 1.81 TB when you check its property on your computer? Here is what it looks like.

To understand what's going on, we need to examine how they advertise and how your computer presents its capacity. We will define key terms and explore the factors that affect storage capacity. We'll take a hands-on approach, with examples and practical formulas to help illustrate the concepts. And, of course, we'll answer some common questions you might have.

Definitions

Let’s get started by understanding the key definitions. Understanding these terms will allow you to perform conversions confidently.

What is claimed capacity

Claimed capacity refers to the total capacity of an SSD or hard disk drive as advertised by the manufacturer, typically measured using decimal (SI) units, which are based on powers of 10.

Here are some examples:

• 128 GB = 128 x 109 = 128,000,000,000 Bytes
• 500 GB = 500 x 109 = 500,000,000,000 Bytes
• 1 TB = 1 x 1012 = 1,000,000,000,000 Bytes

What is real capacity

Real capacity refers to the actual usable storage space of a disk drive after accounting for formatting and system overhead. It differs from the "claimed capacity," which manufacturers advertise using decimal units. It represents the total amount of space available for storing data, as measured by your computer using binary (IEC) units, based on a power of 2.

Here are some examples:

• 128 GB = 128,000,000,000 Bytes ≈ 119.20 GiB
• 500 GB = 128,000,000,000 Bytes ≈ 465.66 GiB
• 1 TB = 1,000,000,000,000 Bytes ≈ 0.9 TiB ≈ 931.32 GiB

Formulas

Let’s take a closer look at the conversion formula so you can carry out these conversions independently, whether using a calculator or doing it manually with pencil and paper.

Claimed to Real Capacity

To calculate the real hard drive capacity from a given claimed capacity, first convert the capacity into bytes, as it is the base unit that remains consistent between decimal and binary measurements.

So, to convert from claimed capacity to byte, multiply the capacity by its decimal multiplier.

Then, convert from bytes to binary units by dividing the number of bytes by the binary multiplier.

Alternatively, we can combine both steps into a simplified formula for easier calculation.

Real to Claimed Capacity

In the opposite situation, when determining the claimed hard drive capacity, first convert the actual capacity into bytes by multiplying it with the appropriate binary multiplier, similar to the previous formula.

Then, convert from bytes to decimal units by dividing the number of bytes by the decimal multiplier.

Or, use the following combined formula.

Examples

Let's examine examples that illustrate the calculations needed to convert a claimed hard disk drive into a real one that shows up on your computer.

Example 1: Calculate the real capacity of a 128 GB solid-state drive.

To calculate the real capacity of a 128 GB drive, use the following formula.

$$\text{Real Capacity} = \frac{\text{Claimed Capacity} \times \text{Decimal Multiplier}}{\text{Binary Multiplier}}$$

Where:

• Claimed Capacity = 128 GB
• Decimal Multiplier of GB = 109 = 1,000,000,000
• Binary Multiplier of GiB = 230 = 1,073,741,824

Now, we can perform the calculation:

$$\text{Real Capacity} = \frac{128 \times 1{,}000{,}000{,}000}{1{,}073{,}741{,}824}$$ $$\text{Real Capacity} = 119.20928955078125 \text{ GB}$$ $$\text{Real Capacity} ≈ \boxed{119.20 \text{ GB}}$$

Therefore, the real capacity of a 128 GB solid state drive that will appear on your computer will be 119.20 GB.

Here is another example required to convert from a computer-listed (Real) capacity to an advertised (Claimed) one.

Example 2: Determine the claimed drive capacity.

Panha, a data engineer, is preparing to store a large dataset for a new project. The dataset size is estimated to be 2 TiB (Tebibytes). Panha needs to determine if the new hard drive claimed to have a capacity of 2 TB (Terabytes) by the manufacturer can store the entire dataset.

To calculate the advertised (claimed) capacity for a 2 TiB data set, use the following formula.

$$\text{Claimed Capacity} = \frac{\text{Real Capacity} \times \text{Binary Multiplier}}{\text{Decimal Multiplier}}$$

Where:

• Real Capacity = 2 TiB
• Binary Multiplier of TiB = 240 = 1,099,511,627,776
• Decimal Multiplier of TB = 1012 = 1,000,000,000,000

Now, we can perform the calculation:

$$\text{Claimed Capacity} = \frac{2 \text{ TiB} \times 1{,}099{,}511{,}627{,}776}{1{,}000{,}000{,}000{,}000}$$ $$\text{Claimed Capacity} = 2.199023255552 \text{ TB}$$ $$\text{Claimed Capacity} ≈ \boxed{2.19 \text{ TB}}$$

Therefore, the hard drive claimed to have a capacity of 2 TB (Terabytes) by the manufacturer is not sufficient to store the entire dataset of 2 TiB (Tebibytes). Panha will need to find a hard drive with at least 2.19 TB (Terabytes) capacity to accommodate the dataset.

Claimed vs. real capacity comparison table

The comparison table below serves as a handy reference for converting advertised disk drive capacities to the actual storage space that appears on your computer. It covers a range from 1 GB to 8 TB, making conversions easy and quick.

Percent difference in binary vs. decimal capacity

The table below shows the percentage difference between decimal and binary units for measuring hard disk drive capacity.

As you can see, the larger the units, the greater the percentage difference between the decimal and binary measurements.

You now know how to convert between an advertised hard disk drive capacity and a real storage space that appears on your computer. You can quickly use our calculator to convert between the drive capacity units to save time for future calculations.

For further understanding, check our data storage converter page to learn more about the differences between decimal and binary units of data storage.