A design check has to come out the same way the second time. The same inputs, the same steps, a result a colleague can follow. That is what a hand calculation is for. A lot of the software around that work spends the hour somewhere else.
A grid hides the step
A spreadsheet can hold a serious design, and many offices already depend on one. The formula sits inside the cell. The units are a label typed next to a bare number. A colleague who opens the file meets references that are hard to read, and a hidden reference is an easy place for an error. The report is a second piece of work. It has to be formatted again, and it drifts as soon as a cell changes.
A worksheet that became harder to use
Mathcad keeps the expression on the page, and the units travel with the number. Mathcad 15 was that tool for a long time. Prime replaced it. For a daily user, the newer program is harder to live in. Files take longer to open. A large worksheet slows down until it is difficult to use. Shortcuts cannot be chosen, and there is no dark theme. Pasting a range from Excel takes more steps than it used to. The program feels far from the engineer who has to finish the check. Years of that daily work are why UnitPad exists.
A language still needs units
A programming language can express the check. Python is the usual next step. Units are the piece it leaves to a package. An engineer wants 6 m and 25 kN/m to multiply, and wants a force added to a length to fail out loud. The package, the environment, and a reader who can run the script then become part of the calculation. The unit check belongs in the language from the start.
The sheet
UnitPad is that sheet, made by Structona. The calculation is written as text. A heading, a named input, an expression. The value appears beside the line and updates when an input changes.
# Simply supported beam L = 6 m q = 25 kN/m M_max = q * L^2 / 8
The engine covers ordinary math, trigonometry, built-in functions, and functions defined on the sheet, together with vectors, plots, and tables. Units are checked as the line is read. A mismatch is an error on that line.
The report comes from the same sheet. Headings, figures, and tables export to PDF. The free sheet uses the default layout and keeps a small UnitPad footer. Pro adds a table of contents, lists of figures and tables, type, color, widths, and the firm’s logo. Pro also brings a Mathcad Prime worksheet in, and sends the sheet out to Excel or Mathcad, so a calculation that already exists can move without being typed again from a blank page.
The file is plain text, .upad or .calc.md, and it stays on the engineer’s own device. The calculation engine is free in the browser and on the desktop, including commercial work. No account is required to calculate.
An assistant, still under review
Because the file is text, an assistant can work on it. On the desktop, Pro connects an assistant already in use, such as Claude, Cursor, VS Code Copilot, or Claude Code, through a local MCP server. It can add a line, change one, or remove one: bring an older check up to a newer code, add an input the verification was missing, or point to the step that does not balance. Each edit arrives as a suggestion. The engineer accepts it or rejects it. The judgment stays with the person responsible for the work.
Try a check you already know
A sheet a colleague can read is the one a team can reuse. UnitPad is built for that, and it is still being improved. Open UnitPad and run a calculation that is already familiar. Notes on what should be clearer are welcome on the contact page.