Why do I need to stretch watercolour paper?

Paper absorbs water and expands unevenly, causing buckling and cockling. Stretching wets the paper fully, then holds it flat as it dries. When you paint on stretched paper, it stays flat because it cannot expand further.

Do I need to stretch heavy paper?

Paper of 300 gsm and above is less prone to buckling and many artists skip stretching. However, heavy washes on any weight can cause cockling. If in doubt, stretch it. 190 gsm paper should always be stretched.

What is the best stretching method?

Gummed tape (brown gumstrip) is the traditional method and works reliably. Stapling is faster but leaves holes. Clips and stretcher frames are reusable but may not hold heavy papers. For beginners, gummed tape is recommended.

How long should I soak the paper?

St Cuthberts Mill (maker of Saunders Waterford and Bockingford) advises about 3 minutes for 190 gsm and about 8 minutes for 300 gsm in clean, cold water. Heavy 425-640 gsm needs a little longer (roughly 10-14 minutes). The clock is only a guide — the real sign it is ready is the sheet going floppy and limp, like wet cloth. Do not over-soak: excessive soaking washes the gelatine size out of modern mould-made paper and weakens the surface.

How long until I can paint on it?

St Cuthberts Mill simply advises leaving the board to dry overnight before painting (about 8 hours for 300 gsm). Drying time is approximate and depends on humidity and temperature, ranging from a few hours for light paper to most of a day for very heavy sheets. Do not use a hairdryer — uneven drying causes warping. Let it dry naturally, flat and horizontal.

ArtCalcs

Paper Stretch Calculator — Watercolour Paper Stretching

Calculate gummed tape length and soaking time for stretching watercolour paper.

Paper Width

Width of the sheet you are stretching (e.g. 380 mm for a quarter-imperial sheet)

Paper Height

Height of the sheet you are stretching (e.g. 280 mm for a quarter-imperial sheet)

Paper WeightPaper weight in grams per square metre

Stretch MethodChoose how you will hold the paper to the board: gummed kraft tape or staples

How We Calculate This

How Paper Stretching Calculation Works

Tape length = Paper perimeter + Overlap allowance

The perimeter of the paper (2 × width + 2 × height) plus the chosen overlap allowance gives the length of gummed tape needed. St Cuthberts Mill advises laying the tape with at least 1 cm on the paper and 1 cm on the board, so a small allowance per side is added. The board should extend at least 20 mm beyond the paper on all sides. Soak time is based on paper weight (about 3 min for 190 gsm, 8 min for 300 gsm, per St Cuthberts Mill); drying time is an approximate guide only — overnight is the manufacturer baseline and the figure varies with humidity and temperature.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify quantities before purchasing materials.