Weight and height.

• It weighs about 3.5 kilos.
• It is about 3.5 kilos in weight.

Weigh is a verb. Weight is a noun.

• How heavy is the kakapo? / How much does the kakapo weigh?
• It weighs about 3.5 kilos.

Also:

• It is 30 cm long.
• It is 30 cm in length.

Long is an adjective and adverb. Length is a noun.

• How long is the kakapo?
• It is 60 cm long. / It is 60 cm in length.

Other words like long – length:

high – height
deep – depth
wide – width

Use tall when you are talking about the height of people:

• How tall is she?
• She is 175 cm tall.

For things and for animals you can also use the verb measure:

• It measures 60 cm in length.
• It measures 30 cm in height.