5 Unit Conversion Mistakes That Caused Real Disasters

A misplaced decimal or a mixed-up unit sounds like a minor slip. In these 5 documented cases, it destroyed a spacecraft, nearly crashed a passenger jet, and cost millions of dollars. Here’s what actually happened, and how to avoid the same category of mistake yourself.

1. NASA’s $125 million Mars Climate Orbiter (1999)

Lockheed Martin’s engineering team calculated thruster data in pound-seconds (imperial units), while NASA’s navigation team expected the values in newton-seconds (metric). The mismatch went undetected through months of course corrections, sending the spacecraft off course by about 60 miles. It burned up in the Martian atmosphere instead of entering orbit.

2. Air Canada’s “Gimli Glider” (1983)

Ground crew calculated the fuel needed for a Boeing 767 in pounds, but Canada had just switched to metric and the aircraft’s fuel systems used kilograms. The plane took off with less than half the fuel it needed and ran out mid-flight. The pilots managed to glide the aircraft to an emergency landing on a former airstrip in Gimli, Manitoba, with no fatalities.

3. USS Yorktown’s dead-in-the-water incident (1997)

A crew member entered a zero into a database field expecting a value within a specific range. The software attempted to divide by that zero, causing a system failure that shut down the ship’s propulsion for nearly three hours.

4. Rocket booster specification confusion

A documented engineering case involved a solid rocket booster specified to produce 10 million pounds of thrust. If that figure were mistakenly read or entered as 10 million Newtons instead, of pounds, the resulting thrust calculation would be off by more than a factor of four, since one pound-force equals roughly 4.45 Newtons.

5. Medical dosing errors from unit mix-ups

Confusing milligrams with micrograms, a thousand-fold difference, has been documented as a recurring source of medication dosing errors in hospital settings. This is a major reason modern electronic prescribing systems now require dose units to be stored as machine-validated codes rather than free-text entry.

What these disasters have in common

Every case above involves two systems or teams exchanging a number without clearly confirming the unit attached to it. The math itself was correct; the unit assumption wasn’t. Much of this friction exists simply because a handful of countries still use imperial units alongside a metric world.

Everyday unit conversion mistakes (lower stakes, still common)

Mistake	Example	Fix
Confusing similar abbreviations	mg vs g, mm vs m	Read abbreviations carefully; double-check before calculating
Converting one unit but not related ones	Changing speed without updating distance/time	Convert every related unit together, not in isolation
US vs UK unit differences	A UK gallon ≠ a US gallon	Confirm which regional system applies
Squaring conversion factors incorrectly	Converting km² to m² using the linear factor instead of squaring it	Square (or cube) the conversion factor for area and volume, not just the linear factor

For quick, accurate conversions across length, weight, temperature, and volume, use our unit conversion calculator instead of converting by hand.

What caused the Mars Climate Orbiter to be lost?

A mismatch between imperial units (pound-seconds) used by the engineering contractor and metric units (newton-seconds) expected by NASA’s navigation team, which went undetected through months of trajectory corrections.

Why did the Gimli Glider run out of fuel?

Ground crew calculated the required fuel in pounds during Canada’s transition to the metric system, while the aircraft’s systems used kilograms, resulting in roughly half the needed fuel being loaded.

What’s the most common everyday unit conversion mistake?

Confusing similarly named or abbreviated units, like milligrams and grams, or forgetting that area and volume conversions require squaring or cubing the linear conversion factor rather than applying it directly.