How to obtain the size in bytes of a certain specific rows of a table

I have created a project where I will offer several stores the opportunity to publish their products and charge them based on the Megabytes they occupy in storage. For this purpose, I am using an SQL database. My question is, how can I obtain the space occupied by a customer in my database if the "products" table has the following columns: "productId", "customerId", "productName", "productPrice"?

I have tried this but it returns the total size of the entire table and what I want is to get the size of certain rows where "customerId" is equal to the requested.

SELECT (SUM(DATA_LENGTH) + SUM(INDEX_LENGTH)) AS 'bytes'
FROM information_schema.TABLES
WHERE TABLE_SCHEMA = 'project' AND TABLE_NAME = 'products';

If you have a better idea to solve this I would greatly appreciate it.

If we can consider that the rows are all the same size, this could work:

The idea is to count the rows per customer, divide by the total number of rows, and multiply the result by the total number of bytes.

with cte as (
  select count(1) as totalData, s.bytes
  from products
  inner join (
    SELECT (SUM(DATA_LENGTH) + SUM(INDEX_LENGTH)) AS 'bytes'
    FROM information_schema.TABLES
    WHERE TABLE_SCHEMA = 'project' and TABLE_NAME = 'products'
  ) as s on true
)
select customer_id, (count(1)/totalData)*c.bytes as totalBytes
from products
inner join cte c on true
group by customer_id