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amcgough14-Alexandrite
14-Alexandrite
Nov 14, 2026 1:24 AM UTC

How Do I Convert N to kg in Mathcad, and How Do I Add the Unit ksc (kg/cm²)?

Scenario / Question

I am working in PTC Mathcad Prime and I need my results in kilograms rather than newtons, so I want Mathcad to treat 1 kilogram as 9.81 newtons. I also need to display pressure results in ksc (kg/cm²), but that unit does not appear in Mathcad's unit list. How do I convert between N and kg, and how do I add ksc to my worksheet?

Overview

You cannot convert newtons to kilograms in Mathcad, because mass and force are different physical dimensions and 1 kg does not equal 9.81 N. You can instead use kilogram-force (kgf), a force unit that is already built into Mathcad Prime, where the factor of roughly 9.81 is standard gravitational acceleration. The unit ksc, kilogram-force per square centimeter, is not predefined in Prime, so you must define it yourself as a user-defined unit and apply the unit label to it.

Step-by-Step

Option 1: Display a force result in kilogram-force instead of newtons

  1. Evaluate the force expression: Enter your expression and add the evaluation operator so the result appears with a unit placeholder.
  2. Clear the existing unit: Click to the right of the displayed unit and press Backspace until the unit disappears. The result turns gray.
  3. Type kgf in the placeholder: Enter kgf, the built-in kilogram-force unit, and press Enter. Mathcad rebalances the units and recalculates the displayed value.
  4. Be explicit about mass versus force elsewhere in the sheet: Use kg only for mass and kgf only for force. In USCS, use lbm for mass and lbf for force, never plain lb.. Mathcad recognizes all of these units.

Note: kgf is a force unit, not a mass unit. A result in newtons can be displayed in kgf, but a result in kilograms cannot, because the two have different dimensions.

Option 2: Define ksc (kg/cm²) as a user-defined pressure unit

  1. Create a definitions area at the top of the worksheet: Place the unit definitions in an area at the top of the sheet and collapse it. Do not use a global assignment for this.
  2. Define ksc in terms of built-in units: Enter ksc, then the definition operator, then kgf divided by cm squared, since ksc is defined as kilogram-force per square centimetre.
  3. Apply the unit label to the name: With the name ksc selected, apply the Unit label from the Math tab labeling options. Mathcad only treats the new name as a unit, and only performs unit checking on it, once the unit label is applied.
  4. Use ksc in a unit placeholder: Evaluate a pressure result, delete the displayed unit, type ksc, and press Enter. The result is shown in kilogram-force per square centimetre.

Key Notes & Limitations

  • There is no N to kg conversion. Mass is not force. The 9.81 factor people expect is standard gravitational acceleration, which converts kilogram-force to newtons, not kilograms to newtons.
  • kgf, also historically called the kilopond, is predefined in PTC Mathcad Prime, as is lbf.
  • ksc is not predefined in Prime. Any pressure unit that is not predefined has to be created as a user-defined unit.
  • A user-defined unit is defined exactly the way a variable is defined. Without the unit label applied to the name, Mathcad will not recognize it as a unit and will not carry out unit checking against it.
  • Defining custom units inside a collapsed area at the top of the worksheet, rather than as a global assignment, keeps the sheet readable and keeps evaluation order predictable.
  • Defining a name that collides with a built-in unit will shadow that unit for the rest of the worksheet, so choose custom unit names carefully.

Related Questions (FAQ)

Q: Can I just tell Mathcad that 1 kg = 9.81 N?

A: No. That equation is dimensionally invalid, because kilogram is a unit of mass and newton is a unit of force. The relationship you are looking for is between kilogram-force and newton, and Mathcad already knows it through the built-in unit kgf.

Q: Is kgf built into PTC Mathcad Prime?

A: Yes. kgf is predefined in Prime, as are lbm and lbf, so you can type them straight into a unit placeholder without defining anything.

Q: Why does ksc not appear in the Mathcad units list?

A: ksc, kilogram-force per square centimeter, is not one of the predefined units in Prime as it is an older, deprecated metric unit of pressure. You can define it yourself as kgf divided by cm squared and apply the unit label to the name.

Q: What does applying the unit label actually do?

A: It tells Mathcad the name is a unit rather than an ordinary variable, which is what allows Mathcad to perform dimensional checking and to display results in that unit.

Links & Resources

This article is part of a new community content management program to bring more visibility to popular posts on the community.  It has been reviewed for accuracy by Andy McGough, Product Management Director.

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