diff --git a/app/javascript/mastodon/utils/resize_image.js b/app/javascript/mastodon/utils/resize_image.js
index 279a858ca..d1608094f 100644
--- a/app/javascript/mastodon/utils/resize_image.js
+++ b/app/javascript/mastodon/utils/resize_image.js
@@ -1,6 +1,6 @@
 import EXIF from 'exif-js';
 
-const MAX_IMAGE_DIMENSION = 1280;
+const MAX_IMAGE_PIXELS = 1638400; // 1280x1280px
 
 const getImageUrl = inputFile => new Promise((resolve, reject) => {
   if (window.URL && URL.createObjectURL) {
@@ -73,18 +73,8 @@ const processImage = (img, { width, height, orientation, type = 'image/png' }) =
 const resizeImage = (img, type = 'image/png') => new Promise((resolve, reject) => {
   const { width, height } = img;
 
-  let newWidth, newHeight;
-
-  if (width > height) {
-    newHeight = height * MAX_IMAGE_DIMENSION / width;
-    newWidth  = MAX_IMAGE_DIMENSION;
-  } else if (height > width) {
-    newWidth  = width * MAX_IMAGE_DIMENSION / height;
-    newHeight = MAX_IMAGE_DIMENSION;
-  } else {
-    newWidth  = MAX_IMAGE_DIMENSION;
-    newHeight = MAX_IMAGE_DIMENSION;
-  }
+  const newWidth  = Math.round(Math.sqrt(MAX_IMAGE_PIXELS * (width / height)));
+  const newHeight = Math.round(Math.sqrt(MAX_IMAGE_PIXELS * (height / width)));
 
   getOrientation(img, type)
     .then(orientation => processImage(img, {
@@ -104,7 +94,7 @@ export default inputFile => new Promise((resolve, reject) => {
   }
 
   loadImage(inputFile).then(img => {
-    if (img.width < MAX_IMAGE_DIMENSION && img.height < MAX_IMAGE_DIMENSION) {
+    if (img.width * img.height < MAX_IMAGE_PIXELS) {
       resolve(inputFile);
       return;
     }
diff --git a/app/models/media_attachment.rb b/app/models/media_attachment.rb
index f9a8f322e..63c6d5af8 100644
--- a/app/models/media_attachment.rb
+++ b/app/models/media_attachment.rb
@@ -32,12 +32,12 @@ class MediaAttachment < ApplicationRecord
 
   IMAGE_STYLES = {
     original: {
-      geometry: '1280x1280>',
+      pixels: 1_638_400, # 1280x1280px
       file_geometry_parser: FastGeometryParser,
     },
 
     small: {
-      geometry: '400x400>',
+      pixels: 160_000, # 400x400px
       file_geometry_parser: FastGeometryParser,
     },
   }.freeze
@@ -152,7 +152,7 @@ class MediaAttachment < ApplicationRecord
       elsif VIDEO_MIME_TYPES.include? f.file_content_type
         [:video_transcoder]
       else
-        [:thumbnail]
+        [:lazy_thumbnail]
       end
     end
   end
diff --git a/lib/paperclip/lazy_thumbnail.rb b/lib/paperclip/lazy_thumbnail.rb
index aafa21343..ea675a5bf 100644
--- a/lib/paperclip/lazy_thumbnail.rb
+++ b/lib/paperclip/lazy_thumbnail.rb
@@ -5,8 +5,14 @@ module Paperclip
     def make
       return File.open(@file.path) unless needs_convert?
 
-      min_side = [@current_geometry.width, @current_geometry.height].min
-      options[:geometry] = "#{min_side.to_i}x#{min_side.to_i}#" if @target_geometry.square? && min_side < @target_geometry.width
+      if options[:geometry]
+        min_side = [@current_geometry.width, @current_geometry.height].min.to_i
+        options[:geometry] = "#{min_side}x#{min_side}#" if @target_geometry.square? && min_side < @target_geometry.width
+      elsif options[:pixels]
+        width  = Math.sqrt(options[:pixels] * (@current_geometry.width.to_f / @current_geometry.height.to_f)).round.to_i
+        height = Math.sqrt(options[:pixels] * (@current_geometry.height.to_f / @current_geometry.width.to_f)).round.to_i
+        options[:geometry] = "#{width}x#{height}>"
+      end
 
       Paperclip::Thumbnail.make(file, options, attachment)
     end
@@ -18,7 +24,8 @@ module Paperclip
     end
 
     def needs_different_geometry?
-      !@target_geometry.nil? && @current_geometry.width != @target_geometry.width && @current_geometry.height != @target_geometry.height
+      (options[:geometry] && @current_geometry.width != @target_geometry.width && @current_geometry.height != @target_geometry.height) ||
+        (options[:pixels] && @current_geometry.width * @current_geometry.height > options[:pixels])
     end
 
     def needs_different_format?
diff --git a/spec/models/media_attachment_spec.rb b/spec/models/media_attachment_spec.rb
index d2230b6d0..cb1cee518 100644
--- a/spec/models/media_attachment_spec.rb
+++ b/spec/models/media_attachment_spec.rb
@@ -129,9 +129,9 @@ RSpec.describe MediaAttachment, type: :model do
       expect(media.file.meta["original"]["width"]).to eq 600
       expect(media.file.meta["original"]["height"]).to eq 400
       expect(media.file.meta["original"]["aspect"]).to eq 1.5
-      expect(media.file.meta["small"]["width"]).to eq 400
-      expect(media.file.meta["small"]["height"]).to eq 267
-      expect(media.file.meta["small"]["aspect"]).to eq 400.0/267
+      expect(media.file.meta["small"]["width"]).to eq 490
+      expect(media.file.meta["small"]["height"]).to eq 327
+      expect(media.file.meta["small"]["aspect"]).to eq 490.0/327
     end
   end