In SQL, units per transaction for the whole period is ROUND(1.0 * SUM(units_sold) / SUM(orders), 2) over the monthly table. On the sample data it returns 1.68.
Units per transaction = Units sold ÷ Number of orders
What you need
Units per transaction (UPT), also called basket size, is the average number of items in each order: total units sold divided by total orders. You need these columns, here from the sample file monthly.csv:
- orders: orders
- units_sold: units sold
CREATE TABLE monthly (
month TEXT, -- 'YYYY-MM'
orders INTEGER,
units_sold INTEGER
);Step by step
- Load monthly.csv into a table called monthly. The table only needs the month column and the columns below.
- Run the first query to get one row per month.
- Run the whole-period query. It adds up each column first and divides once; averaging the monthly results gives a different, usually wrong, answer.
The queries
SELECT
month,
ROUND(1.0 * units_sold / NULLIF(orders, 0), 2) AS units_per_order
FROM monthly
ORDER BY month;SELECT ROUND(1.0 * SUM(units_sold) / NULLIF(SUM(orders), 0), 2) AS units_per_order
FROM monthly;What you should get
Run against the sample data, the code above returns these values:
| Month | orders | units_sold | units_per_order |
|---|---|---|---|
| 2026-01 | 702 | 1,180 | 1.68 |
| 2026-02 | 748 | 1,250 | 1.67 |
| 2026-03 | 812 | 1,370 | 1.69 |
| 2026-04 | 771 | 1,290 | 1.67 |
| 2026-05 | 846 | 1,420 | 1.68 |
| 2026-06 | 917 | 1,530 | 1.67 |
| Whole period | 4,796 | 8,040 | 1.68 |
8,040 ÷ 4,796 = 1.68
Notes for SQL
- Integer columns divide as integers in PostgreSQL, SQLite and SQL Server, so 3 / 4 gives 0. Multiplying by 1.0 (or 100.0) first makes the division decimal.
- NULLIF(x, 0) turns a zero denominator into NULL, so the query returns NULL for that row instead of failing with a division-by-zero error.
- Tested on SQLite and DuckDB. SUM, NULLIF and ROUND work the same in PostgreSQL, MySQL and BigQuery; SQL Server uses TOP instead of LIMIT where a query has one.
Where units per transaction misleads
- Decide how a multipack counts. A pack of three sold as one SKU is one unit to the warehouse and three to the customer; pick one and keep it.
- Free gifts added to an order inflate units without adding revenue. Exclude them or track them separately.
- Returned units should come off the total if you report UPT after returns; otherwise say it is gross.
The full explanation, with a calculator, is on the Units per transaction (UPT) page.
Same metric, other tools
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Learn more about SQL
- Python and SQL for data analysis, side by side — 3 min read
- How to find out what changed in your sales data — 2 min read
About the data on this page
The figures come from a small made-up dataset, printed above in full so you can check every number by hand. Download it as monthly.csv. The results are computed from those rows when the page is built, and the Excel formulas, SQL and Python on these pages are run against the same rows before publishing, so the code and the answers agree.
To get these numbers from your own data without writing formulas, try AnalyzeIt: ask in plain words and it shows the working behind every figure.
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