✉️ C4 Envelope
| Millimeters | 229 × 324 mm |
| Centimeters | 22.9 × 32.4 cm |
| Inches | 9.02 × 12.76 in |
| Points | 649 × 918 pt |
| Picas | 54.1 × 76.5 pc |
| Pixels (300dpi) | 2705 × 3827 px |
| Pixels (72ppi) | 649 × 918 px |
✉️ C5 Envelope
| Millimeters | 162 × 229 mm |
| Centimeters | 16.2 × 22.9 cm |
| Inches | 6.38 × 9.02 in |
| Points | 459 × 649 pt |
| Picas | 38.3 × 54.1 pc |
| Pixels (300dpi) | 1913 × 2705 px |
| Pixels (72ppi) | 459 × 649 px |
Area: 1 C4 = 2 × C5 (C5 is half the area). Scaling factor: 1/√2 ≈ 0.7071 per side.
C5 is the standard invitation and flyer envelope size — this tool helps you scale down from C4 for professional mail and correspondence.
C5 = C4 × 2 · Scale factor = 1/√2 ≈ 0.7071 per side1 C4 envelope splits into exactly 2 C5 envelopes (or 1 C5 = 0.5 C4).
📏 What is C4 Envelope Size?
C4 is a medium envelope size in the ISO 216 C-series. Its dimensions are 229 × 324 mm (9.0 × 12.8 inches), with an area of 0.074 m². C4 is designed to hold A4 paper without folding (A4 is 210 × 297 mm). It's the standard envelope size for professional correspondence, business mail, and official documents. C4 is exactly double the area of C5, making it the most common professional envelope size worldwide.
📄 What is C5 Envelope Size?
C5 is a medium-small envelope size in the ISO 216 C-series. Its dimensions are 162 × 229 mm (6.4 × 9.0 inches), with an area of 0.037 m². C5 is designed to hold A5 paper without folding (A5 is 148 × 210 mm). It's commonly used for invitations, flyers, greeting cards, and smaller professional mail. C5 is exactly half the area of C4, making it a popular choice for premium invitations and marketing materials.
🧮 The Math: How C4 Becomes C5
The ISO 216 C-series is based on the geometric mean of the A and B-series. Each step down (C4 → C5) halves the area. The side lengths decrease by a factor of 1/√2 ≈ 0.7071.
- Width: 229 mm × (1/√2) ≈ 162 mm
- Height: 324 mm × (1/√2) ≈ 229 mm
- Area: 0.074 m² ÷ 2 = 0.037 m²
Formula: 1 C4 = 2 × C5 (in area). So, if you have 1 C4 envelope, you can create 2 C5 envelopes from it (or 1 C5 = 0.5 C4).
📊 Quick Conversion Table: C4 to C5
| C4 Envelopes | C5 Equivalent | Scale factor (side) | Real‑world use |
|---|---|---|---|
| 0.5 C4 | 1 C5 | 100% | Single invitation envelope |
| 1 C4 | 2 C5 | 70.7% (reduce) | Two invitation envelopes |
| 2 C4 | 4 C5 | 50% (half width/height) | Four invitation envelopes |
| 5 C4 | 10 C5 | 31.6% | Bulk mailing |
| 10 C4 | 20 C5 | 22.4% | Large mailing campaign |
| 25 C4 | 50 C5 | 14.1% | Marketing mailer |
| 50 C4 | 100 C5 | 10% | Large-scale mail |
| 100 C4 | 200 C5 | 7.1% | Massive mailing |
✉️ Real‑World Examples: C4 to C5 in Action
- 💌 Invitations & Announcements: C4 is often used for formal invitations and announcements. C5 is used for reply envelopes and thank-you notes. Understanding the scaling helps with consistent branding.
- 📬 Marketing Materials: C4 flyers and brochures can be designed, and then the same artwork can be scaled to C5 for smaller-format mailers or handouts.
- 🏢 Office Correspondence: C4 is the standard for business letters and official documents. C5 is used for smaller correspondence and internal memos.
- 🖨️ Printing & Production: Understanding C4 to C5 conversion is essential for print production, especially when printing multiple envelope sizes from the same sheet.
- 🎨 Art & Photography: C4 is used for standard art prints and portfolios. C5 offers a smaller format for postcards and invitations.
💡 Professional Tips for C4 to C5 Scaling
🎯 Resolution & Quality
When scaling from C4 to C5, if your original is 300 DPI, the resulting C5 will be ~424 DPI — actually higher quality! This is because you're concentrating the same pixels into a smaller area. For best results, design at 300 DPI at C4 for sharp C5 prints.
📐 C‑Series vs. A‑Series
C-series envelopes are designed to fit A-series paper. C4 is designed to hold A4 paper (210 × 297 mm) without folding. C5 holds A5 paper (148 × 210 mm) without folding. This makes C4 the most common business envelope size.
💰 Printing & Mailing Efficiency
Printing 2 C5 envelopes from 1 C4 sheet can save paper and costs. Many professional printers support C-series sizes — check your printer settings for "scale to fit" options.
📂 Professional Correspondence
C4 is the standard for business mail, official documents, and professional correspondence. Use this converter to plan your envelope sizes for professional communications.
❓ Frequently Asked Questions (C4 to C5)
Q: How many C5 envelopes equal 1 C4?
A: Exactly 2 C5 envelopes make 1 C4 in terms of area. You can fit two C5 envelopes on one C4 sheet.
Q: What is the scaling factor from C4 to C5?
A: Each side is scaled by 1/√2 ≈ 0.7071, meaning you reduce the width and height by 29.3%.
Q: Can I fit a C4 document into a C5 envelope?
A: Yes, by scaling it down to 70.7% on each dimension. The document will fit, but text and details will be smaller.
Q: What is the difference in area between C4 and C5?
A: C4 has exactly double the area of C5 (0.074 m² vs. 0.037 m²).
Q: Is C4 bigger than C5?
A: Yes, C4 is larger. C4 is the next size up from C5. 1 C4 = 2 × C5.
Q: What is C4 used for?
A: C4 is used for business mail, official documents, standard invitations, and professional correspondence.
Q: What is C5 used for?
A: C5 is used for invitations, flyers, greeting cards, and smaller professional mail.
Q: Can I print C4 on C5?
A: Yes, by scaling down to 70.7%. Most printers support this scaling. This tool helps you understand the exact ratio.
Q: What is the C‑series used for?
A: C‑series envelopes are designed for flat mail and professional correspondence, holding A‑series paper without folding.
📈 Why Accurate C4‑to‑C5 Conversion Matters
Accurate scaling between C4 and C5 is essential for professional mail, envelope production, and document management. Whether you're preparing an invitation, designing a flyer, or planning a mailing campaign, this tool ensures your envelopes fit perfectly every time. Inaccurate scaling can lead to wasted paper, misaligned designs, and costly reprints.
🌐 Global Standards & Professional Usage
The C‑series (ISO 216) is used alongside the A‑series and B‑series in many countries. C‑series envelopes are specifically designed for flat mail and professional correspondence. C4 is the most widely used business envelope size globally, while C5 is popular for invitations and flyers. This tool supports professional envelope size conversions for users worldwide.
📐 The Full C‑Series Hierarchy
- C8 = 64 × 91 mm – small correspondence
- C7 = 91 × 128 mm – small envelopes, invitations
- C6 = 128 × 182 mm – standard envelopes, invitations
- C5 = 162 × 229 mm – medium envelopes, flyers, invitations
- C4 = 229 × 324 mm – standard mail, A4 documents, business envelopes
- C3 = 324 × 458 mm – large mail, catalogs, A3 documents
- C2 = 458 × 648 mm – oversized mail, A2 documents
- C1 = 648 × 917 mm – very large mail, posters
- C0 = 917 × 1297 mm – extremely large mail, display
Each step up doubles the area, making the system intuitive and easy to scale.
🔗 Explore More Envelope & Mail Tools
Check out our other converters: C5 to C4, C5 to C6, C6 to C5, C3 to C4, C4 to C3, DL to C4, and C4 to DL. All designed to make your print and mail workflows smoother.