We calculate the length of time to help evaluate the impact of an event or era. We can also use this length of time to help us compare two elements.
It is very helpful to compare the lengths of time of the journeys of the great explorers in order to understand how navigation technology changed during the Renaissance.
It’s important to remember that length of time is always expressed as a positive number, even when the dates involved are expressed as negative numbers.
Numerous dates occurred “before Christ” or “before common era.” In these cases, it must always be specified by adding BC or BCE, using a negative sign before the date.
We never speak of a year “0” in history. Our dating system goes from the year -1 straight to the year 1.
To find out more about our calendar and why there is no year 0, see this article.
When calculating the length of a given historical period, we must find the length of elapsed time between two dates (start date and end date). To calculate the difference between the two dates, subtract the oldest date from the most recent date.
Then, choose a unit of time that will express the length of time accurately.
Historical periods such as the Middle Ages wouldn’t be described in terms of months because the length of time is too long. Instead, centuries would be a better measurement of time.
Depending on the case, some lengths of time should be defined in years, months, weeks or days.
Lengths of time that can be calculated in years: wars, revolutions, building construction, life of a public person, recent eras, etc.
Lengths of time that can be calculated in centuries: eras, political regimes, important periods (Renaissance, colonization, Industrial Revolution, etc.)
Lengths of time that can be calculated in months: wars, revolts, etc.
Lengths of time that can be expressed in days: experiments, strikes, popular uprisings, etc.
We must arrive at a positive number, even if we are using dates before Christ / before common era in our calculations.
Start date: -753
End date: 476
Calculation
We calculate by taking the most recent date (476) and subtracting the date that is farther in the past (-753). Be careful! Two negative signs result in a positive sign. So, we obtain:
476 - -753 = 1 229 years
Roman Antiquity lasted about 12 centuries.
Start date: -1200
End date: -146
Calculation
We take the most recent date (-146) and subtract the date that is farthest in the past (-1200). Be careful! Two negative signs result in a positive sign. So, we obtain:
-146 - -1200 = 1 054 years
Greek Antiquity lasted for about 10 centuries.
If we are not sure about our answer, or about which method to use for calculations, we can try calculating the length of time using a timeline. We can use the intervals on the line to easily calculate the interval between the two dates.