Calculadora de Régua (Conversões de Comprimento)
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
mm ↔ cm ↔ in ↔ px via DPI
About this calculator
The Ruler Calculator is an online tool that converts length values between millimeters (mm), centimeters (cm), inches (in), and pixels (px), considering a screen resolution (DPI) provided by the user. It is useful for designers, print professionals, and anyone who needs to relate physical measurements to digital ones, such as when scaling images or layouts.
It works simply: you enter a value in one of the units (mm, cm, in, or px) and inform the resolution in DPI (dots per inch). The calculator applies standard conversions: 1 cm = 10 mm, 1 in = 2.54 cm, and 1 px = 1/DPI inches. Results for all units are displayed instantly, making comparison easy.
Use this calculator when you need to know, for example, how many pixels correspond to 5 cm on a 96 DPI screen, or the size in millimeters of a 300 px image at 300 DPI. It is ideal for adjusting elements in graphic projects, checking print dimensions, or converting physical ruler measurements to digital ones.
Caution: ensure you use the correct DPI for your device or print. Screens typically have 72 or 96 DPI, while prints use 300 DPI or more. Incorrect DPI values lead to wrong conversions. Also, the calculator assumes 1 inch equals exactly 2.54 cm, per international standard.
Frequently asked questions
What is DPI and how do I find the correct value?
DPI stands for dots per inch and defines the resolution of a screen or print. Common screen values are 72 (Mac) or 96 (Windows). For print, use 300 DPI. Check your device or software settings.
Can I convert pixels to centimeters without knowing DPI?
No, converting pixels to physical units depends on DPI. Without that information, the result will be inaccurate. The calculator requires you to provide the DPI.
Does the calculator work for any DPI value?
Yes, you can enter any positive DPI value. The calculator will use that value for all conversions.
What is the difference between mm, cm, and inches?
Millimeters (mm) and centimeters (cm) are metric units, with 1 cm = 10 mm. Inches (in) are imperial, with 1 in = 2.54 cm. The calculator converts between all of them.
Can this calculator be used to calibrate a digital ruler?
Yes, if you know your screen's DPI, you can use the calculator to check the actual size of on-screen elements, helping to calibrate a virtual ruler.