Here in the UK we have a curious mix of units of measurement, some metric, some imperial, which is unique to Britain and reflects the older imperial measurements slowly giving way to considerable use of metric (SI) units of measure, with some notable exceptions stuck in the past.
Length (long distances, journeys) - miles. We describe the distance of a journey from one town to another, or from the UK to another country in terms of miles. Miles are displayed on road signs.
Length (short distances) - metres (m). When talking about short distances such as the distance between buildings, or the dimensions of a room, we use metres, or centimetres / millimetres for much smaller lengths. The one exception is that the height of a person is often still measured in feet (ft) and inches (in), although official measurement (e.g. medical, law enforcement) is in metric.
Length (nautical) - nautical miles (nm). The yachting and maritime community measures distances at sea in nautical miles (1 nm = 1.15 miles).
Length (horses) - hand. The height of a horse is measured in hands, a hand being exactly 4 inches. The world of horse racing is weird and archaic, with several unique units of measurement, including the "length" being 8 feet (or the approximate length of a race horse) and the "furlong" being one eighth of a mile, and used to describe the length of a race course.
Time - hours, minutes, seconds. No surprises here, time is measured in hours, minutes and seconds. The 24 hour clock (in US English called military time) is used in travel timetables, TV guides and other publications. In speech, the am/pm system is used.
Speed (automotive) - miles per hour (mph). The speed of vehicles is measured in miles per hour. Traffic signs display speed limits in mph.
Speed (nautical) - knot (kt or kn). At sea, wind speed and boat speed are both measured in knots (nautical miles per hour). 1 kt = 1.15 mph.
Area (large areas) - square miles (sqm) or square kilometres (sqkm). Large areas, such as the area of a country will normally be measured in square miles, or square kilometres in official publications.
Area (small areas) - acres or hectares (ha). Areas such as building plots or agricultural land is measured in hectares in official communication such as real estate, but informally in conversation acres are often still used.
Volume (objects) - cubic centimetres (cc) or cubic metres (m3). The volume of objects is measured in metric measurements, such as cubic centimetres or cubic metres.
Volume (most liquids) - millilitres (ml), litres (l) or cubic metres (m3). Volume of liquid is measured in metric measurements based on the litre. In cookery, for example, liquid ingredients are measured in millilitres or litres. The US concepts of "cup" and "quart" are not used. Large bodies of water, such as a swimming pool or a lake, are measured in cubic metres. The displacement volume of a car engine is measured in litres or cubic centimetres, for example a car engine might be described as 1.6 l or 1600cc. Automotive fuel is dispensed and purchased in litres. Alcoholic spirits are dispensed in ml.
Volume (beer and cider) - pints. Draught beer and cider is dispensed in imperial pints (0.57 litres). Beer glasses in pubs measure pint or half pint. The British pint is 20% larger than the US pint (0.47 litres).
Alcoholic content - Alcohol by volume (ABV). The measure of alcohol content of a drink is Alcohol By Volume (ABV), expressed as a percentage of the drink that is ethanol. This is true of low alcohol drinks such as beer, as well as wine and spirits. The US measurement of the "proof" of a liquor (being twice the ABV figure, e.g. 40% ABV = 80% proof) is not used in the UK. In the past proof in the UK was defined such that it equalled approximately 1.75x the ABV figure.
Alcohol consumption - Units. In health and medical situations examining consumption of alcohol, this is measured in something called "a unit" being equivalent to 10ml of pure alcohol (ethanol). It is calculated by multiplying the volume of drink (in ml) by its ABV percentage and dividing by 1000. For example, a pint (568 ml) of strong beer (5.2% ABV) equals 2.95 units (i.e. 5.2 * 568 / 1000). The National Health Service advises "men and women are advised not to drink more than 14 units a week on a regular basis" (Source: NHS).
Fuel consumption - miles per gallon. Despite buying fuel in litres, the fuel consumption of a vehicle is still widely described in terms of miles per gallon (4.55 litres). The US Gallon (3.79 litres) is not used at all in the UK. Car manufacturers must also provide fuel efficiency figures in the metric litres per 100km, which is a much more sensible and useful measure for fuel consumption, not widely understood by the British public.
While mass and weight are not the same, outside of scientific sectors, in everyday life they are treated the same. The formal metric measure of weight, the Newton, is not used in everyday life outside of forming part of the definition of torque.
Mass & weight - kilograms (kg). Mass is measured in kilograms, or grams for smaller amounts such as in cooking. The exception is for the mass of a person, which is often also calculated as stone (st) and pounds (lbs), where one stone equals 14 pounds. For example, a 71kg person would not be described as being 157 pounds in the UK, rather as 11st 3lbs. Both methods for weighing people are in use. Some older people might say pounds as a measure of weight when shopping for food and this will be understood, but in law, all prices must be displayed and calculated only in g or kg.
Power (electrical, human) - Watts (W). Power is measured in Watts (or kilowatts or megawatts for higher power figures). This includes all electrical devices and human power output in sport.
Power (automotive) - brake horsepower (bhp). In the UK automotive world, power is described in brake horsepower, although manufacturers will also provide a figure in kilowatts (kW). The older Pferdestärke (PS) was replaced by kW in 1992 but continues to be quoted by some manufacturers.
Energy (science, engineering, electrical) - Joules (J) or kilowatt hours (kWh). Energy in scientific and engineering scenarios is measured in the metric unit of Joules. In domestic and industrial settings, such as electricity consumption, or storage capacity of a battery, kilowatt hours are used.
Energy (food) - Calories (kCal). When describing the energy content of food, it is common in the UK to use Calories, with the meaning of calorie actually being a kilocalorie, i.e. 4184 Joules. kCal and Cal are used synonymously. Energy values of food are often quoted per 100g or 100ml. For example an apple might be said to contain 52 calories per 100g, however the metric value, Joules, is also stated on food packaging.
Torque - Newton Metres (Nm). The torque of cars is measured in Newton Metres.
Temperature - Celsius (°C). Temperatures in the UK are measured in Celsius, for example to describe the weather, for storing and cooking food, and for health. Fahrenheit, once universally used, is now almost entirely restricted to a much older generation referring to the temperature being "in the 80s" or similar. Very few people now use Fahrenheit and weather forecasts and appliances do not refer to it.
Temperature (gas ovens) - Gas Mark. On British gas ovens and in cooking instructions on food packaging, Gas Mark will be used as an alternative temperature scale in parallel with Celsius. Gas Mark 1 = 135 Celsius. It scales linearly with Celsius above 135 °C up to Gas Mark 10 being 270 Celsius.
Currency - Pound Sterling (GBP / £). The British currency is the Pound Sterling. Its ISO code is GBP. The pound is divided into pence. The singular penny has a plural of pence. One pound equals 100 pence.