Free Unit Converter

Free Unit Converter Online

Free Tool Shed's Unit Converter is a comprehensive conversion tool covering 800+ units across 23 categories — from everyday measurements like length and temperature to specialized engineering units like viscosity, thermal conductivity, and torque. Unlike basic converters, it features animated scale visualizations, real-time formula display, batch conversion, and a keyboard-first command palette.

Tips from Building the Unit Converter

Notes from designing and testing this tool — what we kept in mind, the edge cases we worked around, and the small choices that make the difference between a tool that ships and one that breaks on real input.

• Use NIST-sourced factors for engineering work

  Every conversion factor in the tool comes from NIST reference data or published engineering tables. For lab reports or design calculations, this matters — internet-scraped factors often round at the third decimal and accumulate error across multi-step conversions.

• Switch precision based on context

  The tool defaults to 6 significant digits but supports up to 15. Use 4–6 for everyday work; use 12–15 only when you're carrying error through a long calculation chain.

• Batch convert when comparing a range

  When you need the same conversion across many values (10, 20, 50, 100 psi → bar), batch mode runs them all at once instead of you retyping the source value.

• Read the formula bar — it shows the relationship

  The formula display isn't decoration. It shows the actual math (e.g., bar = psi × 0.0689476) so you can verify the conversion is what you expect, or use it in a spreadsheet later.

Common Mistakes to Avoid

• Mixing absolute and gauge pressure

  psi and psia/psig are not interchangeable. Gauge pressure is relative to atmospheric (~14.7 psi). A conversion from "psi" to "bar" gives different answers depending on which the source meant — verify before converting.

• Confusing kg with kgf

  Kilogram is mass; kilogram-force is a weight (mass × g). Engineering calcs often mix them up, producing answers off by ~9.81×. Pick mass units for mass and force units for force.

• Using the wrong temperature scale offset

  Celsius/Fahrenheit conversions are offsets, not ratios. 0°C ≠ 0°F. The tool handles this correctly — but if you're scripting your own conversion, the offset trips most people up.

• Ignoring significant figures from the source

  Converting "3 ft" to "914.4 mm" implies 4-significant-figure precision the source didn't have. Match the output's significant figures to the input's, or your conversion overstates precision.