diff --git a/README.md b/README.md
index 9a9dd07..5e8936a 100644
--- a/README.md
+++ b/README.md
@@ -4,4 +4,129 @@ A plugin for [PostCSS](https://github.com/ai/postcss) that generates viewport un
 
 ## Usage
 
-TODO...
+If your project involves a fixed width, this script will help to convert pixels into viewport units.
+
+### Input/Output
+
+```css
+// input
+
+.class {
+  margin: -10px .5vh;
+  padding: 5vmin 9.5px 1px;
+  border: 3px solid black;
+  border-bottom-width: 1px;
+  font-size: 14px;
+  line-height: 20px;
+}
+
+.class2 {
+  border: 1px solid black;
+  margin-bottom: 1px;
+  font-size: 20px;
+  line-height: 30px;
+}
+
+@media (min-width: 750px) {
+  .class3 {
+    font-size: 16px;
+    line-height: 22px;
+  }
+}
+
+// output
+
+.class {
+  margin: -3.125vw .5vh;
+  padding: 5vmin 2.96875vw 1px;
+  border: 0.9375vw solid black;
+  border-bottom-width: 1px;
+  font-size: 4.375vw;
+  line-height: 6.25vw;
+}
+
+.class2 {
+  border: 1px solid black;
+  margin-bottom: 1px;
+  font-size: 6.25vw;
+  line-height: 9.375vw;
+}
+
+@media (min-width: 234.375vw) {
+  .class3 {
+    font-size: 5vw;
+    line-height: 6.875vw;
+  }
+}
+```
+
+### Example
+
+```js
+'use strict';
+
+var fs = require('fs');
+var postcss = require('postcss');
+var pxToViewport = require('..');
+var css = fs.readFileSync('main.css', 'utf8');
+var options = {
+    replace: false
+};
+var processedCss = postcss(pxToViewport(options)).process(css).css;
+
+fs.writeFile('main-viewport.css', processedCss, function (err) {
+  if (err) {
+    throw err;
+  }
+  console.log('File with viewport units written.');
+});
+```
+
+### Options
+
+Default:
+```js
+{
+  viewportWidth: 320,
+  viewportHeight: 568,
+  unitPrecision: 5,
+  viewportUnit: 'vw',
+  selectorBlackList: [],
+  minPixelValue: 1,
+  mediaQuery: false
+}
+```
+- `viewportWidth` (Number) The width of the viewport.
+- `viewportHeight` (Number) The height of the viewport.
+- `unitPrecision` (Number) The decimal numbers to allow the REM units to grow to.
+- `viewportUnit` (String) Expected units.
+- `selectorBlackList` (Array) The selectors to ignore and leave as px.
+    - If value is string, it checks to see if selector contains the string.
+        - `['body']` will match `.body-class`
+    - If value is regexp, it checks to see if the selector matches the regexp.
+        - `[/^body$/]` will match `body` but not `.body`
+- `minPixelValue` (Number) Set the minimum pixel value to replace.
+- `mediaQuery` (Boolean) Allow px to be converted in media queries.
+
+
+### Use with gulp-postcss
+
+```js
+var gulp = require('gulp');
+var postcss = require('gulp-postcss');
+var pxtoviewport = require('postcss-px-to-viewport');
+
+gulp.task('css', function () {
+
+    var processors = [
+        pxtoviewport({
+            viewportWidth: 320,
+            viewportUnit: 'vmin'
+        })
+    ];
+
+    return gulp.src(['build/css/**/*.css'])
+        .pipe(postcss(processors))
+        .pipe(gulp.dest('build/css'));
+});
+```