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J277 1.2.3 Data units and capacity

Part 5 of 6 · J277 1.2.1-1.2.3 · Memory and storage

Data units and capacity calculations, using decimal arithmetic only so it can be taught before binary conversion.

Students will:

  • explain why computers represent data in binary
  • order the units from bit to petabyte
  • convert between adjacent units using the stated convention
  • calculate a required storage capacity
  • work out how many files fit in the space available

Inside: 6 explanation cells, 4 multiple-choice questions, 1 fill-in-the-blanks cell and 4 written answers. 26 marks, about 60 minutes.

Series: J277 1.2.1-1.2.3 · Memory and storage, part 5 of 6.

Shared by Coding PathwayVerified teacher

  • 15 cells
  • About 60 minutes
  • CC BY-SA 4.0
  • Shared 17 Aug 2026
  • Updated 9 Sept 2026

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The whole resource, exactly as a class sees it. Answers and marking are held back.

Memory and storage 5: data units and capacity

Storage devices have fixed capacities, and files occupy part of that capacity. Data units let us describe and compare these quantities.

This worksheet uses ordinary decimal calculations. Binary conversion, hexadecimal, binary addition and shifts will be taught separately.

By the end of this worksheet, you should be able to:

  • explain why computers represent data in binary
  • order the units bit, nibble, byte, KB, MB, GB, TB and PB
  • move between adjacent storage units using the stated convention
  • calculate a required storage capacity
  • calculate how many files will fit in available space

Work through the explanation, checks and applications in order. Use the final challenge to connect several ideas.

1. Why computers use binary

Electronic computer systems contain circuits that can represent two distinct states, commonly described as on and off. These states can be represented using the binary digits 1 and 0.

Text, images, sound and instructions must therefore be represented in binary before a computer can process them.

A bit is one binary digit. This worksheet concentrates on the amount of storage represented by groups of bits, not on converting binary numbers.

Multiple choice1 mark

Why must data be converted into binary for computer processing?

  • AComputer circuits can represent two states, which can be recorded as 0 and 1
  • BBinary automatically compresses every file
  • CHumans can read binary more easily than ordinary text
  • DBinary gives every storage device unlimited capacity

2. The data-unit scale

From smallest to largest:

  1. bit: one binary digit
  2. nibble: 4 bits
  3. byte: 8 bits
  4. kilobyte (KB): 1,000 bytes
  5. megabyte (MB): 1,000 KB
  6. gigabyte (GB): 1,000 MB
  7. terabyte (TB): 1,000 GB
  8. petabyte (PB): 1,000 TB

OCR accepts calculations using 1,024, but these worksheets will state and use the decimal convention of 1,000 so that each question has one unambiguous answer.

Data-unit scale and decimal conversion direction Four bits make one nibble and eight bits make one byte. Moving from bytes to kilobytes, megabytes, gigabytes and terabytes divides by one thousand each step. Moving towards smaller units multiplies by one thousand. OCR calculations normally use decimal units bytekBMBGBTB ÷ 1000÷ 1000÷ 1000÷ 1000 towards smaller units: multiply by 1000 for each step 4 bits = 1 nibble • 8 bits = 1 byte
Fill in the blanks6 marks
A label 1 is one binary digit. Four bits make a label 2. Eight bits make a label 3. One thousand bytes make a label 4. One thousand megabytes make a label 5, and one thousand terabytes make a label 6.
  • terabyte
  • byte
  • petabyte
  • nibble
  • gigabyte
  • megabyte
  • bit
  • kilobyte
Multiple choice1 mark

Which sequence is ordered from smallest to largest?

  • Abyte, bit, nibble, megabyte, kilobyte
  • Bkilobyte, byte, gigabyte, megabyte, terabyte
  • Cbit, nibble, byte, kilobyte, megabyte
  • Dnibble, bit, byte, gigabyte, megabyte

3. Moving between units

Using 1,000:

  • moving to a smaller unit means multiplying by 1,000
  • moving to a larger unit means dividing by 1,000

Example:

3 GB × 1,000 = 3,000 MB

750,000 KB ÷ 1,000 = 750 MB

Bits and bytes are the exception to the 1,000 pattern:

8 bits = 1 byte

Before calculating, convert all values into the same unit.

Multiple choice1 mark

Using 1 GB = 1,000 MB, how many megabytes are in 4.5 GB?

  • A45 MB
  • B0.0045 MB
  • C450 MB
  • D4,500 MB
Written answer3 marks

Using 1 KB = 1,000 bytes, convert 24,000,000 bits into kilobytes. Show both stages of your working.

First divide by 8 to convert bits to bytes. Then divide by 1,000 to convert bytes to KB.

Students type their answer here.

4. Capacity calculations

Example:

A USB flash drive has 6 GB free. Each video is 250 MB. How many complete videos fit?

  1. Convert the free space: 6 GB × 1,000 = 6,000 MB
  2. Divide by the size of one file: 6,000 ÷ 250 = 24

So, 24 complete videos fit.

If a division gives a decimal, only complete files count unless the question says otherwise. You may need to round down.

Written answer3 marks

A storage device has 12 GB of free space. Each sound file is 80 MB. Using 1 GB = 1,000 MB, calculate how many complete sound files can be stored. Show your working.

Convert the capacity to MB, then divide by the size of one file.

Students type their answer here.

Written answer4 marks

A class produces 28 video files, each 350 MB. Calculate the total capacity required in GB using 1 GB = 1,000 MB. Then state whether they fit in 10 GB of free space.

Multiply the number of files by the size of each file, convert to GB, then compare.

Students type their answer here.

Multiple choice1 mark

A student converts 2 TB to GB by dividing by 1,000. What is the mistake?

  • AThe student should divide by 8
  • BThere is no relationship between TB and GB
  • CMoving from TB to the smaller GB unit requires multiplying by 1,000
  • DThe student should multiply by 4 because a nibble has 4 bits
Written answer6 marks

Challenge: a 32 GB memory card already stores 18 files of 750 MB each. Using 1 GB = 1,000 MB, calculate the remaining capacity in GB and the number of additional 750 MB files that can fit. Show all working.

Convert 32 GB to MB, calculate the existing total, subtract, then divide. Only complete additional files count.

Students type their answer here.

5. Make your method visible

For a capacity question, underline the required final unit, convert all values to the same unit, show the operation, include units and check whether only complete files count. OCR papers do not allow calculators, so clear working is particularly important.

Closed-book review

  1. Why do computers use binary?
  2. Put all eight data units in order.
  3. How many bits are in a nibble?
  4. How many bits are in a byte?
  5. Using 1,000, what operation moves from GB to MB?
  6. What operation moves from KB to MB?
  7. What should you do before comparing a file size and a device capacity?
  8. Why might a final file-count answer need rounding down?