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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: 5 text sections, 3 multiple-choice activities, 5 completion activities, 3 written answers. 20 marks. Suggested teaching time: 40–60 minutes. 1 diagram.

Includes a teacher guide with suggested sections, timings and common misconceptions.

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

Shared by Coding PathwayVerified teacher

  • 16 cells
  • About 45 minutes
  • CC BY-SA 4.0
  • Shared 17 Aug 2026
  • Updated 27 Oct 2026

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

Data units and capacity

Files occupy storage space. Compare a file size with free capacity using the same units.

All calculations here use 1 kB = 1,000 bytes, 1 MB = 1,000 kB, and 1 GB = 1,000 MB. Ignore formatting, headers and other overheads.

1. Bits and bytes

Electronic circuits can represent two distinct states, often described as on and off. We represent these using 1 and 0, so computers represent data in binary.

  • A bit is one binary digit.
  • A nibble is 4 bits.
  • A byte is 8 bits.
Multiple choice1 mark

Why is data represented in binary for computer processing?

  • AElectronic circuits can represent two distinct states
  • BEvery file contains only two characters
  • CBinary gives unlimited storage
  • DA byte contains one bit
Fill in the blanks4 marks
One binary digit is a Answer 1. Four bits form a Answer 2. Eight bits form a Answer 3. One thousand bytes form a Answer 4.
  • bit
  • nibble
  • byte
  • kilobyte
  • megabyte

2. The full scale

bit → nibble → byte → kilobyte (kB) → megabyte (MB) → gigabyte (GB) → terabyte (TB) → petabyte (PB)

From bytes onwards, divide the number by 1,000 for each step to a larger unit. Reverse a step by multiplying by 1,000. Kilobytes are also often written KB. A lowercase b means bits, not bytes.

Decimal unit ladder From byte through kilobyte, megabyte, gigabyte, terabyte and petabyte, divide by 1000 at each step towards a larger unit. Reverse by multiplying by 1000. Four bits form a nibble and eight bits form a byte. byte kB MB GB TB PB To larger units ÷ 1,000 each step Reverse direction × 1,000 each step 4 bits = 1 nibble; 8 bits = 1 byte
Multiple choice1 mark

Which sequence is smallest to largest?

  • AGB, MB, TB, PB
  • BMB, GB, TB, PB
  • CPB, TB, GB, MB
  • DMB, TB, GB, PB

3. Convert before comparing

  • 3 GB × 1,000 = 3,000 MB
  • 750,000 bytes ÷ 1,000 = 750 kB
  • 160 bits ÷ 8 = 20 bytes

Use 8 for bits and bytes. Use 1,000 for decimal steps from bytes onwards.

Fill in the blanks3 marks
Use the decimal convention. (a) 4.5 GB = Answer 1 MB. (b) 2 TB = Answer 2 GB. (c) 160 bits = Answer 3 bytes.
Written answer2 marks

Show the two operations needed to convert 24,000,000 bits to kilobytes, using 8 bits = 1 byte and 1 kB = 1,000 bytes.

Students type their answer here.

Fill in the blanks1 mark
Using 8 bits = 1 byte and 1 kB = 1,000 bytes, 24,000,000 bits = Answer 1 kB.

4. How many complete files fit?

A drive has 6 GB free and each video is 250 MB:

  1. 6 × 1,000 = 6,000 MB free.
  2. 6,000 ÷ 250 = 24 complete videos.

If the result is not a whole number, round down: part of a file is not a complete file.

Written answer2 marks

A device has 12 GB free. Each sound file is 80 MB. Show the operations needed to find how many complete files fit, using 1 GB = 1,000 MB.

Students type their answer here.

Fill in the blanks2 marks
Use 1 GB = 1,000 MB. Count complete files only. (a) 12 GB free, files of 80 MB each: Answer 1 files. (b) 3 GB free, files of 400 MB each: Answer 2 files.
Written answer2 marks

A class makes 28 videos of 350 MB each. Show the operations needed to calculate their total size in GB, using 1 GB = 1,000 MB and ignoring overheads.

Students type their answer here.

Fill in the blanks1 mark
A class makes 28 videos of 350 MB each. Ignore overheads; use 1 GB = 1,000 MB. Total size = Answer 1 GB.
Multiple choice1 mark

A different set of videos totals 9.6 GB. Which statement is correct for a device with 10 GB free?

  • AThey do not fit because 9.6 is larger than 10
  • BThey fit, leaving 0.4 GB
  • CThey fit, leaving 4 GB
  • DThe quantities must be changed to bits first