Engineering Unit Conversion: SI Units, Data Storage, and Common Mistakes

Unit conversion errors have caused real disasters. The Mars Climate Orbiter was lost in 1999 because one team used metric units and another used imperial. A Canadian Boeing 767 ran out of fuel mid-flight in 1983 because of a kilogram/pound confusion. In software, data storage unit mistakes cause capacity planning failures and monitoring alert misconfiguration every day.

SI Units: The Foundation

The International System of Units (SI) defines seven base units from which all other units are derived:

Quantity	Unit	Symbol
Length	meter	m
Mass	kilogram	kg
Time	second	s
Electric current	ampere	A
Temperature	kelvin	K
Amount of substance	mole	mol
Luminous intensity	candela	cd

SI prefixes scale these units by powers of ten:

Prefix	Symbol	Factor
giga	G	10⁹
mega	M	10⁶
kilo	k	10³
milli	m	10⁻³
micro	μ	10⁻⁶
nano	n	10⁻⁹
pico	p	10⁻¹²

Common Engineering Conversions

Length

1 inch   = 25.4 mm = 2.54 cm
1 foot   = 0.3048 m
1 mile   = 1.609344 km
1 yard   = 0.9144 m
1 nautical mile = 1.852 km

Temperature

°F to °C: (°F - 32) × 5/9
°C to °F: (°C × 9/5) + 32
°C to K:  °C + 273.15

Common reference points:

• 0°C = 32°F = 273.15 K (water freezes)
• 100°C = 212°F = 373.15 K (water boils at sea level)
• 37°C = 98.6°F (human body temperature)

Pressure

1 atm = 101,325 Pa = 1013.25 hPa = 14.696 PSI = 1.01325 bar
1 PSI = 6,894.76 Pa = 0.068948 bar
1 bar = 100,000 Pa = 14.5038 PSI

Speed

1 m/s    = 3.6 km/h = 2.237 mph = 1.944 knots
1 km/h   = 0.2778 m/s = 0.6214 mph
1 mph    = 1.609 km/h = 0.447 m/s
1 knot   = 1.852 km/h = 1.151 mph

Data Storage Units: The IEC vs SI Confusion

This is where software engineers get tripped up most often:

SI Prefixes (powers of 10)

1 kilobyte  (kB)  = 1,000 bytes
1 megabyte  (MB)  = 1,000,000 bytes
1 gigabyte  (GB)  = 1,000,000,000 bytes
1 terabyte  (TB)  = 1,000,000,000,000 bytes

IEC Prefixes (powers of 2)

1 kibibyte (KiB) = 1,024 bytes
1 mebibyte (MiB) = 1,048,576 bytes
1 gibibyte (GiB) = 1,073,741,824 bytes
1 tebibyte (TiB) = 1,099,511,627,776 bytes

Why This Matters in Practice

A 500 GB hard drive (SI) contains approximately 465.66 GiB. Operating systems that report in GiB show a smaller number than the marketing claims in GB — hence the "missing" disk space users see after formatting.

In networking, bandwidth is almost always measured in SI units (bits per second), but file sizes may be in either convention depending on the OS and application.

# A common bug: confusing MB and MiB
file_size_bytes = 500 * 1024 * 1024   # 500 MiB
file_size_bytes = 500 * 1000 * 1000   # 500 MB (10.5% smaller)

# For accurate capacity planning, be explicit:
MiB = 1024 ** 2
GiB = 1024 ** 3

allocation = 8 * GiB  # 8,589,934,592 bytes

Network Throughput vs. Storage Capacity

Network speeds are in bits per second (bps), storage in bytes. The conversion:

1 Gbps network = 125 MB/s throughput (÷ 8 bits per byte)

Transfer time = File size (bits) / Bandwidth (bps)
10 GB file on 100 Mbps connection:
= (10 × 10^9 × 8) / (100 × 10^6)
= 800 seconds ≈ 13.3 minutes

Convert Units in Bulk

When you need to convert multiple values across different unit systems — infrastructure capacity planning, lab data processing, hardware specifications — the Batch Unit Converter on InfraHub handles length, mass, temperature, pressure, speed, data storage, and more. Enter a list of values and convert them all at once, entirely in your browser.