Convert TDMS to CSV online

How to convert TDMS to CSV

1. 1Open your .tdms file. Choose it, or drop it on the tool at the top of this page. It opens on the table, on its first group. No file to hand? Click “Try a sample TDMS file”.
2. 2Pick the group. The menu in the file’s line lists the file’s groups; a group with channels of different lengths or rates gives a table for each. “Variables” shows every channel and property first, if you want to check.
3. 3Download the CSV. Click “Download as CSV” over the table. The CSV holds the table’s time column and every channel, every row; for another group or time base, pick it and download again.

A worked example you can check

“Try a sample TDMS file” opens a month of made-up UK weather in three groups, each with its own time base:

• Hourly (744 rows, 5 channels and the time): temperatures in London, Leeds and York, London’s humidity and pressure, every hour from 1 January 2026.
• Rain gauge (4,464 rows, 2 channels and the time): rain in London and Leeds every ten minutes, on its own time base.
• Daily (31 rows, 4 channels and the time): a timestamp channel, Date, which becomes the time axis, the day’s highest and lowest temperature and the weather in words.

It opens on Hourly. Click Download as CSV, and the CSV starts like this:

Time,London_Temperature,Leeds_Temperature,York_Temperature,London_Humidity,London_Pressure
2026-01-01 00:00,5.44,3.32,2.79,93.1,1013
2026-01-01 01:00,4.99,2.93,2.42,92.8,1011.8
2026-01-01 02:00,4.74,2.72,2.2,88,1012.6

Pick Daily in the file’s line and download again: its Date channel is the time column, and the weather in words is a column of text.

Date,London_Max_Temperature,London_Min_Temperature,London_Conditions
2026-01-01,10.54,4.7,Cloudy
2026-01-02,10.77,4.85,Heavy rain

A test opens the sample on every change to the site and checks these lines against what npTDMS, the Python library for TDMS files, reads in it. Download the sample (.tdms, 105 KB) to try it elsewhere too: the same sample TDMS measurement file is free to reuse under CC0.

What the CSV keeps

The time column

The first column is the group’s time. From the waveform properties LabVIEW and DAQmx write, it is the date and time of each value in UTC (2026-01-01 00:00, with seconds or milliseconds when the rate needs them), or seconds from the start when the file has no start time. A group without waveform timing keeps its own time or timestamp channel; with none, the rows are in sample order.

One table per time base

Channels logged at different rates can’t share rows without repeating or inventing values, so each group is its own CSV, and channels of another length or rate inside a group are a table of their own in the menu. No value in the CSV is repeated or invented.

Numbers, booleans and text

Numbers are written with 15 significant digits, the precision Excel writes; tick Full precision (17 digits) under “Do more” for every digit. Booleans are 0 and 1, timestamp channels dates and times, and text is written as it is, in double quotes when it holds a comma.

DAQmx data and NI scales

DAQmx raw data is read with its scalers. Linear and polynomial scales, and sums and differences of scales, are applied. Thermocouple, RTD, strain, thermistor and table scales are not yet: those channels show their stored values, with a note saying so. The CSV holds the same values as the table: scaled, or as stored where a scale isn’t applied yet.

Units and properties

The CSV’s header row holds the channel names only: there is no units row, and no properties. Each channel’s unit (unit_string) shows next to it in the table, and its properties, with those of its group and the file, are listed in Variables.

TDMS to Excel

NI’s free TDM Excel Add-In loads a .tdms file into a workbook on Windows, a sheet per group. The converter here needs no add-in and works on any computer.

Open it in Excel

MegaRows writes CSV, not .xlsx: there is no direct .xlsx download, and Excel opens the CSV directly. To check the separator first, use Data › From Text/CSV in Excel.

• One table per CSV. A group, or one time base of it: a header row of channel names, then the group’s time in the first column when it has one, and a column per channel.
• Channels at different rates. They are never padded or interpolated into one table: channels of another length or rate are a table of their own in the menu of the file’s line, so pick each one and download it too.
• Excel’s row limit. A worksheet holds 1,048,576 rows, the header row included, and Excel cuts off the rest of a longer CSV. Split the CSV into Excel-sized files with the CSV splitter, or keep the file in the TDMS viewer, which has no fixed row limit.
• Saving as .xlsx. If you need a workbook, open the CSV in Excel, then use File › Save As and choose Excel Workbook (.xlsx).

Other ways to convert TDMS to CSV

• LabVIEW or DIAdem can export channels to text files.
• Python: with npTDMS, TdmsFile.read("file.tdms")["Group"].as_dataframe() gives a pandas data frame of a group, and to_csv writes it.
• MATLAB: tdmsread, in the Data Acquisition Toolbox, then writetimetable.

The converter on this page needs none of them. For MATLAB files, use MAT to CSV.

Private by design: nothing is uploaded

Test and measurement data often must not leave the company. This converter reads your .tdms file and writes the CSV in your browser, so the file and its name never leave your device. It handles big files too: a channel’s values are read only when the CSV is written.