Online Activities for 3rd - 6th Classes
Khan Academy - Perimeter (Third Grade): Watch the videos and then answer the practice questions. Afterwards, for something more challenging, look at the Fourth Grade activities on Area and Perimeter, the Metric System and/or Converting Metric Units. Or even the Fifth Grade activities on Converting Metric Length Units. You can also register for a free Khan Academy account to record your progress and explore other topics/grades.
Splash Learn - Measurement Games: These games cover how to measure length, measure the perimeter of regular shapes, the perimeter of non-regular shapes, calculate a side length when given perimeter, calculate the perimeter of simple shapes, perimeter of complex shapes, converting metric units, including metric units with decimals.