Unit Converters
Convert between 345 measurement units across 13 categories — length, mass, temperature, volume, area, speed, and more. Free, instant, NIST-precision calculations.
Precision Unit Conversion — Powered by NIST
OmniConvert's unit converter provides scientifically accurate conversions across 10 categories and 86+ conversion pairs. Every conversion factor is sourced from NIST SP 811 (National Institute of Standards and Technology Special Publication 811), the internationally recognized reference for the International System of Units (SI). Unlike most online converters that use rounded approximations, OmniConvert preserves full decimal precision — critical for engineering calculations, scientific research, and academic work. The converter covers length, mass, temperature, volume, area, time, speed, energy, pressure, and power with support for both SI and imperial units. All calculations run instantly in your browser with zero server dependency, meaning you get real-time results even when offline. Whether you're an engineer verifying tolerances, a student solving physics problems, or a chef scaling recipes, OmniConvert delivers the precision you need.
Length
52 conversions
Mass
44 conversions
Temperature
6 conversions
Volume
46 conversions
Area
26 conversions
Time
30 conversions
Speed
20 conversions
Energy
26 conversions
Pressure
24 conversions
Power
14 conversions
Angle
16 conversions
Digital Storage
29 conversions
Fuel Economy
12 conversions
Popular Conversions
Frequently Asked Questions
What is NIST SP 811?
NIST SP 811 is a publication by the U.S. National Institute of Standards and Technology that provides guidelines for using the International System of Units (SI). It includes precise conversion factors between SI and non-SI units used worldwide.
Why does precision matter in unit conversion?
Rounded conversion factors can introduce cumulative errors in engineering, science, and manufacturing. Using NIST-grade factors ensures results are accurate to the full decimal precision required by professional applications.
How many units does OmniConvert support?
OmniConvert currently supports 10 unit categories with 86+ conversion pairs covering length, mass, temperature, volume, area, time, speed, energy, pressure, and power.
Is an internet connection required?
No. All unit conversions are calculated client-side in your browser. You can install OmniConvert as a PWA and use it completely offline.
Can I use this for professional or academic work?
Yes. The NIST SP 811 conversion factors used by OmniConvert meet the precision requirements for engineering, scientific research, and academic applications.
Values based on NIST SP 811 conversion factors