Excel to JSON Converter - Convert XLSX to JSON Online Free

Last updated March 22, 2026

Excel to JSON Conversion

Converting Excel files (.xlsx, .xls) to JSON makes spreadsheet data accessible to web applications and APIs. Each row in the spreadsheet becomes a JSON object, with column headers as keys. This is a common data migration task when moving from spreadsheet-based workflows to database-driven applications.

Excel File Structure

Modern Excel files (.xlsx) are ZIP archives containing XML files. The main data is in xl/worksheets/sheet1.xml, with shared strings in xl/sharedStrings.xml. Libraries like SheetJS (xlsx) handle this complexity and provide a simple API.

Converting with SheetJS

import * as XLSX from 'xlsx';

async function excelToJson(file) {
  const buffer = await file.arrayBuffer();
  const workbook = XLSX.read(buffer, { type: 'array' });

  const result = {};
  for (const sheetName of workbook.SheetNames) {
    const sheet = workbook.Sheets[sheetName];
    // Convert to array of objects (first row = headers)
    result[sheetName] = XLSX.utils.sheet_to_json(sheet, {
      header: 1,        // use first row as headers
      defval: null,     // default value for empty cells
      blankrows: false  // skip blank rows
    });
  }
  return result;
}

// Usage with file input
document.getElementById('fileInput').addEventListener('change', async (e) => {
  const file = e.target.files[0];
  const json = await excelToJson(file);
  console.log(JSON.stringify(json, null, 2));
});

Data Type Handling

• Dates: Excel stores dates as serial numbers (days since Jan 1, 1900). SheetJS converts them to JavaScript Date objects with cellDates: true.
• Formulas: By default, SheetJS reads the cached formula result. Use raw: false to get formatted values.
• Numbers: Large numbers may lose precision — use dense: true for better handling.