Some non-SI units are accepted for use with the International System of Units (SI). They are given this status because they are useful in many practical everyday applications but are not strictly necessary for pure scientific and engineering work. They are however highly compatible and so do not detract from the advantages of metric, in fact they are very handy and user friendly. Again only select few are shown.
Non-SI units accepted for use with the SI
| Unit name | Symbol | Definition and what is measured |
|---|---|---|
| minute | min | Time = 60 s |
| hour | h | Time = 60 min = 3 600 s |
| day | d | Time = 24 h = 86 400 s |
| hectare | ha | Area = 1 hm2 = 10 000 m2 Used for land areas |
| litre | l or L | Volume = 1000 cm3 = 0.001 m3 = 1 dm3 (cubic decimetre) The familiar litre in which we buy petrol, etc. Note that (for all practical everyday purposes) 1 litre of pure liquid water has a mass of 1 kg |
| tonne | t | Mass = 1000 kg Used in transport, vehicle masses and weight limits, etc. Also the approximate mass of one cubic metre of water (see litre above) |
Other non-SI units
| Unit name | Symbol | Definition and what is measured |
|---|---|---|
| bar | bar | Pressure = 100 kPa = 1000 hPa Used in weather mapping (mbar) |
UK Metric Association 