diff --git a/src/routes/upload.ts b/src/routes/upload.ts
index 4981e66..2247c84 100644
--- a/src/routes/upload.ts
+++ b/src/routes/upload.ts
@@ -8,7 +8,7 @@ import {
     ValidationError,
 } from '../errors.js';
 import { config } from '../config.js';
-import { save } from '../store.js';
+import { getTakenQuota, save } from '../store.js';
 
 type UploadPayload = {
     data: string; // base64-encoded
diff --git a/src/store.ts b/src/store.ts
index e257cea..317e677 100644
--- a/src/store.ts
+++ b/src/store.ts
@@ -3,14 +3,62 @@ import { config } from './config.js';
 import path from 'path';
 import fsp from 'node:fs/promises';
 
+function getClient(
+    clientName: string,
+): { name: string; quota: number } | undefined {
+    const client = config.clients.find((x) => x.name === clientName) as
+        | { name: string; quota: number; keySha256Sum?: string }
+        | undefined;
+
+    delete client?.keySha256Sum;
+    return client;
+}
+
+function getClientOrThrowErr(
+    clientName: string,
+    error?: string,
+): { name: string; quota: number } {
+    const client = getClient(clientName);
+    if (typeof client === 'undefined')
+        throw Error(error ?? 'Client does not exist.');
+    return client;
+}
+
 export function getPathFor(name: string, clientName: string): string {
     return path.join(config.storePath, clientName + '-' + name);
 }
 
+export async function getFilesFor(clientName: string): Promise<string[]> {
+    const files = await fsp.readdir(config.storePath);
+    return files.filter((x) => x.startsWith(clientName + '-'));
+}
+
+/**
+ * @returns { number } In megabytes
+ */
+export async function getTakenQuota(clientName: string): Promise<number> {
+    const files = await getFilesFor(clientName);
+    const stats = await Promise.all(
+        files.map((x) => fsp.stat(path.join(config.storePath, x))),
+    );
+
+    let size = 0;
+    stats.forEach((x) => (size += x.size));
+
+    return size / 1000000;
+}
+
 export async function save(
-    data: string | Buffer | NodeJS.ArrayBufferView,
+    data: Buffer,
     name: string,
     clientName: string,
-): Promise<undefined> {
+): Promise<undefined | 'Quota exceeded'> {
+    const client = getClientOrThrowErr(clientName);
+    const quota = await getTakenQuota(clientName);
+
+    if (data.length + quota > client.quota) {
+        return 'Quota exceeded';
+    }
+
     await fsp.writeFile(getPathFor(name, clientName), data);
 }