Add Percent of Total to CSV Files Online

What does percent of total calculate in a CSV file?

For each row, it divides the row's value by the sum of that column across all rows (or within a group), then multiplies by 100. The result is a new column showing each row's share as a percentage — equivalent to col / SUM(col) OVER () * 100.

Can I calculate percent of total within groups in a CSV file?

Yes. Set a Partition By column and each row's percentage is calculated relative to the group total rather than the grand total. For example, each product's share of its own category's revenue rather than its share of all revenue.

Does the percent of total column sum to exactly 100 in a CSV file?

It sums to 100 when there are no null values in the column. Null rows are excluded from both the numerator and denominator. To include nulls in the total, use the Fill Empty Values tool to replace them with 0 before computing percentages.

Is my data private?

Yes — completely. Your file is never uploaded to any server. Everything runs locally in your browser using WebAssembly — processing happens entirely inside your tab. Once you close the tab, nothing is retained.

What is the maximum file size?

The free limit is 50 MB. For larger files, performance depends on your device's available memory — most modern machines handle 500 MB to 1 GB comfortably.