Memorize Unit Conversions: 96 Metric & Imperial Flashcards Built on a Dozen Anchors

Most people who "can't do unit conversions" actually lack about a dozen anchor numbers. The Unit Conversions: Metric & Imperial deck (code EY8789, 96 cards) holds all of them, plus prefixes, temperature formulas and some physics units. Here is how to memorize it so you can work out the rest instead of storing every pair.

Cards worth knowing cold

What the 96 cards cover

Length (inch, foot, yard, mile, nautical mile), mass (ounce, pound, stone, short ton, tonne), US kitchen volume (fluid ounce, cup, pint, quart, gallon, tablespoon, teaspoon) and the Imperial gallon, area (ft², m², acre, hectare), the cubic meter and cubic foot, °F/°C/K and absolute zero, mph and km/h, horsepower and watts, BTU, calorie and kilocalorie, atm, bar, PSI and pascals, STP and molar volume, the SI prefixes from nano- to giga-, plus light-year, AU, parsec and angstrom.

Study plan: anchors first, then derive

1. Learn the exact definitions as one group. Since 1959 the inch is defined as exactly 2.54 cm, so the foot (×12), yard (×3) and mile (×5,280) all follow. Run cards 2-5 and 7-9 together until you can rebuild each one from the inch. Do the same with cards 66-73: once you have the prefixes, cards 10-12, 17-18, 24 and 74-77 only test them again.

2. Fix four "≈" backs on your copy. The deck marks some values as approximate when they are exact by definition. The pound is exactly 0.45359237 kg (card 13), the nautical mile exactly 1.852 km (cards 49-50), and the US gallon exactly 3.785411784 L (231 in³, card 23). Write "exactly" into those backs and you know which numbers you can never get wrong.

3. Treat temperature as a pair of formulas. Cards 30-35 say the same thing three ways. Keep 34 and 35 (the formulas) and add one check card: −40 °F = −40 °C, where the two scales meet. If your formula doesn't return −40, you mixed up the order of operations.

Cards to update or merge

• Cards 63-64 (STP) give 0 °C and 1 atm with 22.414 L/mol. That is the pre-1982 convention. IUPAC's current STP is 100 kPa, which gives ≈ 22.711 L/mol. Tag the card with the convention your course uses.
• Card 89 counts a year as 365 days. Add the Julian year (365.25 d ≈ 31,557,600 s), which is the year used to define the light-year in card 82.
• Cards 24 and 95 are duplicates. Keep the question version.
• The deck gives the Imperial gallon but not the Imperial pint (568 mL), which is the UK beer pint. Add it next to card 21.

Practice it in Flip It

Find EY8789 — Unit Conversions: Metric & Imperial in the Flip It library. Want more number fluency? Pair it with how to memorize mathematical constants, squares, cubes and roots.