Complete Unit Conversion Chart: Length, Weight, Area, Volume & Temperature
Let me tell you why I keep a grimy, photocopied conversion chart taped inside my kitchen cabinet. It’s because I once tried to double a recipe that called for a “cup” of flour, and I used my 8-ounce coffee mug. The resulting brick of “bread” could have doubled as a doorstop. That’s the moment I learned the hard way that a “cup” is a specific volume measurement, not just any old container.
Unit conversions aren’t about academic perfection. They’re about not ruining dinner, ordering the right amount of flooring, or figuring out if the 37-degree Celsius weather means shorts or a sweater. The theory is simple: multiply or divide by a number. The real-world mess is in remembering which number, and when.
So, let’s break down the five conversions you’ll actually bump into, with the shortcuts that work when you’re in the grocery store aisle or staring at a foreign thermometer.
The Mental Shortcuts I Actually Use
I don’t memorize every single conversion. I memorize one anchor point for each category and work from there.
Length: The Rule of Thumb
For inches to centimeters, your thumb knuckle to the tip is about an inch (2.54 cm, to be precise). My anchor? One foot is roughly 30 centimeters. One meter is about 3.3 feet. So, if a room is 6 meters long, that’s about 20 feet (6 x 3.3). It’s not NASA-exact, but it’s perfect for eyeballing furniture or understanding a product description.
Where people mess up: Assuming it’s a clean 10:1 ratio. It’s not “10 cm = 1 inch,” it’s 2.54. That difference compounds. A 6-foot man isn’t 180 cm (which would be 5'11"), he's about 183 cm.
Weight/Mass: The Grocery Store Divide
In the US, you buy meat in pounds. Almost everywhere else, it’s in kilograms. My anchor: 1 kilogram is a little over 2 pounds (2.2 lbs, exactly). So, a 5kg bag of rice is about 11 pounds. To go from pounds to kilos, I just cut the pounds in half and subtract a little. 10 lbs is about 4.5 kg (half of 10 is 5, subtract a bit).
Common misconception: Weight and mass are technically different (thanks, gravity), but for 99% of daily life—cooking, postage, your body weight—we use them interchangeably. Don’t let that confusion stop you.
Volume: The Cooking Catastrophe Zone
This is where my bread brick was born. The big divide is between the US Customary system (cups, gallons) and liters. My anchor: 1 liter is a little more than 1 US quart (1.06 quarts). A gallon is about 3.8 liters. For cooking, remember: 1 cup = 240 milliliters. Not 250, not 200. That 10 ml difference can throw off baking chemistry.
Personal failure story: I once tried to use a liquid measuring cup (the clear one with a spout) for flour. I scooped it right out of the bag. That packs the flour in. You’re supposed to spoon it in gently. That “cup” was probably 20% more flour than intended. My cookies spread into one sad, giant cookie-sheet.
Area: The Home Project Headache
You need this for paint, flooring, or land. From square feet to square meters, the multiplier isn’t the same as for length. My anchor: 10 square feet is about 1 square meter (0.93 sq m, to be precise). So, a 300 sq ft room is roughly 30 sq meters. This is the one I always double-check with a calculator because the cost of being wrong is high—you’re either stuck with half a room unfinished or you’ve wasted $200 on extra flooring.
Temperature: The “What to Wear” Gauge
Fahrenheit to Celsius is the weird one. The formulas look scary (°C = (°F - 32) / 1.8). I think in benchmarks:
0°C = 32°F (Freezing. Ice.)
10°C = 50°F (Chilly jacket weather)
20°C = 68°F (Pleasant room temperature)
30°C = 86°F (Hot summer day)
37°C = 98.6°F (Body temperature)
My quick-and-dirty method for the weather: Take the °F, subtract 30, then halve it. 80°F? 80-30=50, halve it to 25°C. (Actual: 26.7°C). Close enough to know if you need sunscreen.
What To Be Careful About
“Imperial” vs. “US Customary”: They’re almost the same, but not quite. A UK (Imperial) pint is 20 oz. A US pint is 16 oz. That matters a lot if you’re following a British recipe or, more importantly, ordering a beer in London. If a source doesn’t specify, assume US.
Dry vs. Liquid Volume: In the US system, they’re measured differently. A dry gallon isn’t the same as a liquid gallon. Thankfully, you’ll almost never see “dry gallons” outside of agriculture. Just be aware the word “gallon” alone usually means the liquid one.
Online Calculators are Your Friend, But… They are perfect for precision. Use them for anything involving money or materials. But develop your anchor-point mental math for everything else—it builds intuition and saves you from obvious errors, like thinking a 50°C day is pleasant (it’s 122°F, you’d melt).
At the end of the day, conversion isn’t about math purity. It’s about translating the world into units your gut understands. Tape a chart somewhere you’ll see it. Screw up a recipe once or twice. You’ll remember those numbers far better than any perfect, polished table.