Mismeasurement

A character confuses measurements in some activity, resulting in having too little or too much of something that will become disastrous.

Maybe involve Explosive Stupidity in regards to the amount of gunpowder used, or Oven Logic.

Examples of Mismeasurement include:

Comic Books

In the Polish Kajko i Kokosz comic books the evil knights would construct a siege tower to get over the town wall but at night the heroes would sneak into the knights' encampment and alter the plans just enough to foil the plan. Since the knights were too stupid to recheck the measurements they would end up with a ramp that was too short or too long and Hilarity Ensued.

In the film The Black Bird (a sequel/parody of The Maltese Falcon), the eponymous statue is mismeasured; it's one cubit long, about the length of a man's forearm, but the man who was measuring it is a Little Person so his arm is much shorter than normal.

This was a feature of many of Bergholt Stuttley "Bloody Stupid" Johnson's inventions on the Discworld.

Jonathan Creek: In "Angel Hair", Jonathan is designing an illusion that centres around sawing a ventiloquist dummy in half. As the trick requires extra sets of feet for the dummy, he tells the dummy maker to be sure dummy has twelve feet. The dummy maker ends up delivering a 12 foot tall dummy.
An episode of The Cosby Show had Theo ask his older sister if she could tailor a fake designer shirt for him (he had previously claimed he owned one in order to impress a girl). Her measurments are off, resulting in the shirt having oddly lengthed sleeves and other obvious mistakes in measurements.

This Is Spinal Tap: due to confusion on the symbols for feet (') and inches ("), a Stonehenge prop that was supposed to be 18 feet tall was instead 18 inches, and nearly stomped on by the little people actors onstage.

A Garfield strip had Jon asking Garfield about the right amount of chili powder to add to a dish that he was making. The resulting amount caused the entire dish to go poof (It might have been intentional, as Garfield then tells Jon to pitch it all out and order a pizza).

Ghost Trick: in the ending, Beauty and Dandy are breaking into a safe above Chicken Kitchen with gunpowder. Dandy reads the instructions for twenty kilograms of gunpowder instead of twenty grams.

The protagonist of the children cartoon Jimbo is a talking Jumbo-jet that was manufactured in centimetres instead of inches by mistake.
In the episode of Hey Arnold! where they try to get into the world record book, their attempt at the largest pizza pocket fails when Sid misinterprets "tsp" as "ten square pounds".
The Simpsons: Homer is in the basement trying to invent something. He works out a few equations on the chalkboard, hammers, saws, welds, and finally blows up the basement. Walking over to a chart, he changes a "greater than" sign to a "less than" sign, and goes back to work.
- In another episode, Mr. Burns drops a weight on Homer, but it's 1000 grams. That's about 2.2 pounds, which did not have the desired affect. Burns curses the metric system.

The Mars Climate Orbiter ended up being lost in space because its software expected thruster performance to be entered in metric units, but the ground crew used imperial units.
The "Gimli Glider" was an incident in July 1983 where a Air Canada Boeing 767-200 jet run out of fuel while an route from Montreal to Edmonton and had to be piloted as a glider and landed at an abandoned air strip In Gimli, Manitoba. The problem was traced to the use of an incorrect conversion factor for calculating the weight of a litre of fuel in kilograms. Canada was switching to the metric system at the time and a conversion factor for the weight in pounds was used instead.