Count Distinct in Data Studio: Why Unique Users Don't Add Up

• Unique counts are not additive
• Watch table totals
• Avoid averaging unique counts
• Say which one you mean

One of the most common questions I get on Data Studio (formerly Looker Studio) reports is why the daily user numbers don’t add up to the monthly total. I’m Harsh Khubchandani, an independent Data Studio consultant in New Delhi, and this is how I explain it.

§Unique counts are not additive

A person who visits on Monday and Tuesday is one user for the week but appears in both daily counts. So the sum of daily users is almost always higher than the weekly or monthly figure. Neither number is wrong; they answer different questions.

§Watch table totals

When a table shows unique users by channel, the total row may not equal the sum of the rows, because one person can arrive through more than one channel. I either hide the total row or add a short note explaining it.

§Avoid averaging unique counts

Averaging a unique count across rows or blending it with another source can produce numbers that mean nothing. When a client needs something like average daily users, I make sure the calculation is clearly labelled and checked against the source.

§Say which one you mean

In the metric definitions page of a report I state whether a user figure is for the selected date range as a whole or summed by day. That one line saves a lot of back and forth.

More notes on clear reporting at datastudioconsultant.com.