diff --git a/lib/appender-adapter.js b/lib/appender-adapter.js
new file mode 100644
index 0000000..c6b3eb1
--- /dev/null
+++ b/lib/appender-adapter.js
@@ -0,0 +1,49 @@
+function maxFileSizeUnitTransform(maxLogSize) {
+  if (typeof maxLogSize === 'number' && Number.isInteger(maxLogSize)) {
+    return maxLogSize;
+  }
+
+  const units = {
+    K: 1024,
+    M: 1024 * 1024,
+    G: 1024 * 1024 * 1024,
+  };
+  const validUnit = Object.keys(units);
+  const unit = maxLogSize.substr(maxLogSize.length - 1).toLocaleUpperCase();
+  const value = maxLogSize.substring(0, maxLogSize.length - 1).trim();
+
+  if (validUnit.indexOf(unit) < 0 || !Number.isInteger(Number(value))) {
+    throw Error(`maxLogSize: "${maxLogSize}" is invalid`);
+  } else {
+    return value * units[unit];
+  }
+}
+
+function adapter(configAdapter, config) {
+  Object.keys(configAdapter).forEach((key) => {
+    if (config[key]) {
+      config[key] = configAdapter[key](config[key]);
+    }
+  });
+}
+
+function fileAppenderAdapter(config) {
+  const configAdapter = {
+    maxLogSize: maxFileSizeUnitTransform
+  };
+  adapter(configAdapter, config);
+}
+
+function fileSyncAppenderAdapter(config) {
+  const configAdapter = {
+    maxLogSize: maxFileSizeUnitTransform
+  };
+  adapter(configAdapter, config);
+}
+
+const appenderAdapter = {
+  file: fileAppenderAdapter,
+  fileSync: fileSyncAppenderAdapter
+};
+
+module.exports = appenderAdapter;
diff --git a/lib/configuration.js b/lib/configuration.js
index c520c5c..e73b5f6 100644
--- a/lib/configuration.js
+++ b/lib/configuration.js
@@ -4,6 +4,7 @@ const util = require('util');
 const path = require('path');
 const levels = require('./levels');
 const layouts = require('./layouts');
+const appenderAdapter = require('./appender-adapter');
 const debug = require('debug')('log4js:configuration');
 
 let cluster;
@@ -69,6 +70,11 @@ class Configuration {
 
   createAppender(name, config) {
     const appenderModule = this.loadAppenderModule(config.type);
+
+    if (appenderAdapter[config.type]) {
+      appenderAdapter[config.type](config);
+    }
+
     this.throwExceptionIf(
       not(appenderModule),
       `appender "${name}" is not valid (type "${config.type}" could not be found)`
diff --git a/test/tap/fileAppender-test.js b/test/tap/fileAppender-test.js
index 39b0394..cb933a9 100644
--- a/test/tap/fileAppender-test.js
+++ b/test/tap/fileAppender-test.js
@@ -110,6 +110,49 @@ test('log4js fileAppender', (batch) => {
     }, 100);
   });
 
+  batch.test('with a max file size in unit mode and no backups', (t) => {
+    const testFile = path.join(__dirname, 'fa-maxFileSize-unit-test.log');
+    const logger = log4js.getLogger('max-file-size-unit');
+
+    t.tearDown(() => {
+      removeFile(testFile);
+      removeFile(`${testFile}.1`);
+    });
+    removeFile(testFile);
+    removeFile(`${testFile}.1`);
+
+    // log file of 1K = 1024 bytes maximum, no backups
+    log4js.configure({
+      appenders: {
+        file: {
+          type: 'file', filename: testFile, maxLogSize: '1K', backups: 0
+        }
+      },
+      categories: {
+        default: { appenders: ['file'], level: 'debug' }
+      }
+    });
+    const maxLine = 13;
+    for (let i = 0; i < maxLine; i++) {
+      logger.info('This is the first log message.');
+    }
+
+    logger.info('This is the second log message.');
+
+    // wait for the file system to catch up
+    setTimeout(() => {
+      fs.readFile(testFile, 'utf8', (err, fileContents) => {
+        t.include(fileContents, 'This is the second log message.');
+        t.equal(fileContents.indexOf('This is the first log message.'), -1);
+        fs.readdir(__dirname, (e, files) => {
+          const logFiles = files.filter(file => file.includes('fa-maxFileSize-unit-test.log'));
+          t.equal(logFiles.length, 2, 'should be 2 files');
+          t.end();
+        });
+      });
+    }, 100);
+  });
+
   batch.test('with a max file size and 2 backups', (t) => {
     const testFile = path.join(__dirname, 'fa-maxFileSize-with-backups-test.log');
     const logger = log4js.getLogger('max-file-size-backups');
diff --git a/test/tap/fileSyncAppender-test.js b/test/tap/fileSyncAppender-test.js
index 869618d..195a012 100644
--- a/test/tap/fileSyncAppender-test.js
+++ b/test/tap/fileSyncAppender-test.js
@@ -84,6 +84,52 @@ test('log4js fileSyncAppender', (batch) => {
     t.end();
   });
 
+  batch.test('with a max file size in unit mode and no backups', (t) => {
+    const testFile = path.join(__dirname, '/fa-maxFileSize-unit-sync-test.log');
+    const logger = log4js.getLogger('max-file-size-unit');
+
+    remove(testFile);
+    remove(`${testFile}.1`);
+
+    t.tearDown(() => {
+      remove(testFile);
+      remove(`${testFile}.1`);
+    });
+
+    // log file of 100 bytes maximum, no backups
+    log4js.configure({
+      appenders: {
+        sync: {
+          type: 'fileSync', filename: testFile, maxLogSize: '1K', backups: 0
+        }
+      },
+      categories: { default: { appenders: ['sync'], level: 'debug' } }
+    });
+    const maxLine = 13;
+    for (let i = 0; i < maxLine; i++) {
+      logger.info('This is the first log message.');
+    }
+
+    logger.info('This is the second log message.');
+
+    t.test('log file should only contain the second message', (assert) => {
+      fs.readFile(testFile, 'utf8', (err, fileContents) => {
+        assert.include(fileContents, `This is the second log message.${EOL}`);
+        assert.equal(fileContents.indexOf('This is the first log message.'), -1);
+        assert.end();
+      });
+    });
+
+    t.test('there should be two test files', (assert) => {
+      fs.readdir(__dirname, (err, files) => {
+        const logFiles = files.filter(file => file.includes('fa-maxFileSize-unit-sync-test.log'));
+        assert.equal(logFiles.length, 2);
+        assert.end();
+      });
+    });
+    t.end();
+  });
+
   batch.test('with a max file size and 2 backups', (t) => {
     const testFile = path.join(__dirname, '/fa-maxFileSize-with-backups-sync-test.log');
     const logger = log4js.getLogger('max-file-size-backups');
diff --git a/types/log4js.d.ts b/types/log4js.d.ts
index 6ae3a53..b812c88 100644
--- a/types/log4js.d.ts
+++ b/types/log4js.d.ts
@@ -107,7 +107,7 @@ export interface FileAppender {
 	// the path of the file where you want your logs written.
 	filename: string;
 	// the maximum size (in bytes) for the log file. If not specified, then no log rolling will happen.
-	maxLogSize?: number;
+	maxLogSize?: number | string;
 	// (default value = 5) - the number of old log files to keep during log rolling.
 	backups?: number;
 	// defaults to basic layout
@@ -126,7 +126,7 @@ export interface SyncfileAppender {
 	// the path of the file where you want your logs written.
 	filename: string;
 	// the maximum size (in bytes) for the log file. If not specified, then no log rolling will happen.
-	maxLogSize?: number;
+	maxLogSize?: number | string;
 	// (default value = 5) - the number of old log files to keep during log rolling.
 	backups?: number;
 	// defaults to basic layout