Free craft tool · Flat cards
Envelope Punch Board Calculator
Enter your finished card size for a square-paper and first-score estimate. Start with scrap paper, then check the fit before cutting your final stock.
Read the method and limitsYour flat card
Measure the finished, closed card. Each edge: 1–12 inches. Use decimals, for example 4.25 for 4¼.
Either edge order works. Unit switching preserves your original measurement; metric display uses up to 6 decimal places.
Or choose a card size
US stationery sizes, not ISO paper sizes.
Your starting estimate
Flat cards only. Not a manufacturer chart or a tested fit. Try scrap paper first.
Quick Reference: The Envelope Punch Board Formula
Square Paper Cut Size
Paper Size = (Card Short Edge + Card Long Edge) ÷ √2 + 1.0″Result is rounded up to the nearest ⅛″ for smooth card insertion.First Score Line on Ruler
First Score = Card Short Edge ÷ √2 + 0.5″Result is rounded to the nearest ⅛″ ruler tick. Only the first edge uses the ruler.Why divide by √2? Because the paper is placed at a 45° diagonal on the board, the Pythagorean relationship converts rectangular card edges into diagonal folding coordinates (1 ÷ sin 45° ≈ 1.4142).
Method & limits
This is an independent flat-card estimator, not an official We R Memory Keepers chart. It uses a 45-degree model with fixed allowances: paper = (short + long) ÷ √2 + 1″; first score = short ÷ √2 + ½″. Paper rounds up to ⅛″; the first score rounds to the nearest ⅛″.
The A2 starting pair (8″ paper, 3½″ score) and A7 starting pair (9½″ paper, 4″ score) agree with A Matter of Squeak’s independent examples. That comparison does not validate every custom size or board. No Letter Ritual physical fold tests have been completed.
Board offsets, paper thickness, long narrow cards and rounding can change clearance or flap alignment. Check that your board can reach the first mark. Thick cards and 3D boxes are not supported.
Try one scrap-paper envelope first
1. Cut a test square
Measure your card closed. Cut inexpensive paper to the estimated square size. Keep your final decorative paper aside.
2. Make the first mark
Follow your board’s instructions to align at the first score measurement, punch and score. If the ruler cannot reach the mark, stop and use a board-specific method.
3. Rotate and align
On boards that use a score-guide pointer, rotate 90 degrees and align the previous score line to the pointer. Repeat according to the manufacturer’s instructions.
4. Check before gluing
Fold the test envelope and insert the card. Check corner clearance, closure and flap alignment. If it pinches or will not close, do not use the estimate on final stock.
Flat-card reference estimates
The table and calculator share the same calculation. Card names use US stationery sizing, not ISO paper sizes. On a small screen, scroll the table sideways.
| Card | Closed card size | Paper · each side | First score | Sheet fit |
|---|---|---|---|---|
| A2 Card | 4 1/4″ × 5 1/2″ | 8″ | 3 1/2″ | Can be trimmed from US Letter, A4 or 12×12″ paper. |
| A7 (5×7) | 5″ × 7″ | 9 1/2″ | 4″ | Can be trimmed from 12×12″ paper; too wide for US Letter and A4. |
| US A6 Card | 4 1/2″ × 6 1/4″ | 8 5/8″ | 3 5/8″ | Can be trimmed from 12×12″ paper; too wide for US Letter and A4. |
| 4×6 Photo | 4″ × 6″ | 8 1/8″ | 3 3/8″ | Can be trimmed from US Letter, A4 or 12×12″ paper. |
| Square 5×5 | 5″ × 5″ | 8 1/8″ | 4″ | Can be trimmed from US Letter, A4 or 12×12″ paper. |
| Slimline | 3 1/2″ × 8 1/2″ | 9 1/2″ | 3″ | Can be trimmed from 12×12″ paper; too wide for US Letter and A4. |
| Small Note 3½×5 | 3 1/2″ × 5″ | 7 1/8″ | 3″ | Can be trimmed from US Letter, A4 or 12×12″ paper. |
Common questions
What is the mathematical formula for an envelope punch board?
Because punch boards score along 45-degree diagonal axes, the geometry uses dividing by √2 (approx. 1.4142). The flat-card formulas are: Square Paper Size = (Card Short Edge + Card Long Edge) ÷ √2 + 1.0 inch (rounded up to the next ⅛ inch); First Score Line = Card Short Edge ÷ √2 + 0.5 inch (rounded to the nearest ⅛ inch).
How are these measurements estimated?
For flat cards, square paper = (short edge + long edge) ÷ √2 + 1 inch, rounded up to the next ⅛ inch. First score = short edge ÷ √2 + ½ inch, rounded to the nearest ⅛ inch. The fixed allowances are a starting assumption, not a manufacturer calibration. Board geometry, paper thickness and rounding can affect fit. Test on scrap paper first.
What is the A2 card starting estimate?
For a US A2 card measuring 4¼ × 5½ inches, this calculator estimates an 8 × 8 inch paper square and a 3½ inch first score. These two measurements agree with A Matter of Squeak’s independent A2 tutorial example, not an official manufacturer chart. Letter Ritual has not physically fold-tested this result.
Can I use this for thick cards or 3D boxes?
No. This version supports flat cards only. Embellished cards, stacked inserts and box envelopes need a thickness-aware method that has not been validated here.
Are the presets international paper standards?
No. A2, A6 and A7 here are US stationery card sizes, not ISO A-series paper. Always check the displayed card dimensions. Enter the finished, closed card size, not the unfolded sheet or the outside envelope size.