Magento – Magento2 : How to get product dimension units (cm/in)

I guess there would be some extention for your need but i just let you know my opinion without extension. First of all, you need to add attribute. Go to Catalog > Attributes > Manage Attributes.

And you can add new attribute you would use for weight unit and you can edit some options on Attribute Information > Manage Label/Option. You can add Oz, Kgs, Lbs, packets and grams for grocery.

And then, go to Catalog > Attributes > Manage Attribute Sets and make 'Grocery' attribute. Then, you can add attribute you need.

Or,you can change the property of weight attribute like text input. There is a way to write unit directly for each product.

The attributes ts_dimensions_length / ts_dimensions_width / ts_dimensions_height are part of the Temando_Shipping module that ships with Magento 2.

[ Source: Line 32 - 34 in vendor/temando/module-shipping-m2/Setup/SetupData.php ]

You should be able to get their values by using the code snippet below:

$product->getTsDimensionsLength();
$product->getTsDimensionsWidth();
$product->getTsDimensionsHeight();