How do I convert this unit?

One meter is 3.280839895 feet, because the foot is defined as exactly 0.3048 meters. The familiar shortcut "a meter is about 3.28 feet" is fine for a room; rounding it to 3 is not, since that undercounts by more than 9%. Going the other way, one foot is 30.48 cm exactly. Both of these are definitions agreed in the 1959 international yard and pound agreement, not measurements, so they carry no uncertainty at all.

Multiply kilograms by 2.20462262 to get pounds, or divide pounds by that same number to go back. The exact definition runs the other way: one pound is exactly 0.45359237 kilograms. For mental math, doubling and adding 10% gets you within half a percent — 70 kg → 140 + 14 = 154 lb, against a true 154.32 lb. In the UK you may also need stone: 14 pounds to the stone, so 154 lb is 11 st 0 lb.

An ounce is a unit of weight, exactly 28.349523125 grams. A US fluid ounce is a unit of volume, 29.5735 milliliters. They only coincide for water, and even then only by rough accident, which is exactly why recipes go wrong. If a recipe asks for 8 oz of flour it wants 227 grams on a scale; if it asks for 8 fl oz it wants one US cup, which is closer to 120 grams of flour. Weighing removes the ambiguity entirely.

The troy ounce is the surviving unit of a separate medieval weight system kept alive for precious metals. It is 31.1034768 grams against the avoirdupois ounce's 28.349523125 grams, about 10% heavier. Gold, silver, platinum and palladium are all quoted per troy ounce, so using the kitchen ounce to value bullion underprices it by roughly a tenth. A troy pound, confusingly, is only 12 troy ounces and is lighter than a normal pound.

Multiply square feet by 0.09290304, or divide by 10.763910417. The factor is the length factor squared: 0.3048² = 0.09290304 exactly. The most common mistake in real estate listings is dividing by 3.28 instead, which inflates the metric area by more than three times. As a sanity check, a 1,000 ft² apartment is about 93 m², and a 100 m² apartment is about 1,076 ft².

No, and the gap is large enough to matter. The US gallon is 3.785411784 liters; the imperial gallon used in the UK and Canada is 4.54609 liters — about 20% bigger. That difference propagates through every subdivision: a US pint is 473 mL while an imperial pint is 568 mL, and a US fluid ounce is 29.57 mL against the imperial 28.41 mL. Fuel-economy figures in miles per gallon are therefore not comparable across the Atlantic without conversion.

It is shorthand for BTU per hour, a rate of heat removal. One BTU per hour is 0.293 watts and 0.252 kilocalories per hour, which is what Spanish-language labels call a frigoría. A "one-ton" unit is defined as 12,000 BTU/h, roughly 3.52 kW, from the rate that would melt a short ton of ice in a day. Crucially this is cooling capacity, not electricity drawn: an efficient 12,000 BTU/h unit consumes around 1 kW from the wall.

In dilute water solutions, yes, exactly — because one liter of water has a mass of one kilogram, one milligram per liter is one milligram per million milligrams, which is one part per million. That is why US water quality reports switch between the two labels without comment. The equivalence breaks as soon as the solution density stops matching water, and it does not apply at all to gases in air, where ppm is a volume ratio.

Subtract 32, then multiply by 5/9. Going the other way, multiply by 9/5 and add 32. Temperature is the one conversion in this hub that is not a simple multiplication, because the two scales have different zero points as well as different step sizes. Handy anchors: water freezes at 32 °F / 0 °C, room temperature is 68 °F / 20 °C, body temperature is 98.6 °F / 37 °C, and the two scales cross at −40°.

The metric quintal is 100 kilograms, so ten quintals make one metric ton and a yield of 45 qq/ha is 4.5 t/ha. Be careful with the word outside that metric context: the old Spanish and Portuguese quintal was around 46 kg, and several countries kept local versions. Contracts should always state the kilogram equivalent, and this converter uses the metric 100 kg definition throughout.

Because the factor was rounded somewhere along the way. If you multiply by 3.28 to get feet and divide by 3.28 to get back, you land on your starting number — but neither figure was ever right, because the true factor is 3.280839895. This converter stores the exact defined factor for every unit and always routes through the family's base unit, so a round trip is an exact inverse and only display rounding is visible.

A hectare is 10,000 square meters, which is a square 100 m on a side. An acre is 43,560 square feet, or 4,046.856 square meters — historically the area one ox team could plow in a day, which is why it is not a round number. One hectare is 2.4711 acres, and one acre is 0.4047 hectares. For a fast field estimate, a hectare is about two and a half acres, and an acre is a bit smaller than an American football field without the end zones.