Why do I run out of wash mid-way?

The most common reason is not mixing enough wash before starting. Once you begin a flat wash, you cannot stop to mix more without creating a hard edge. Always mix more than you think you need — at least 30% extra as a buffer. Leftover wash can be saved in a sealed jar.

What is the paint-to-water ratio for a medium wash?

A medium-strength wash uses approximately 3% paint to water by volume. For a light wash, use about 1%. For a strong, saturated wash, use up to 6%. These are approximate — the exact ratio depends on the pigment concentration of your particular paint brand.

Does paper weight affect wash volume?

Yes. Heavier paper (300gsm+) absorbs more water and needs a larger volume of wash. Lighter paper (190gsm) absorbs less but is more prone to cockling. This calculator adjusts the volume based on your paper weight to account for absorbency differences.

How do I keep a flat wash even?

Work at a slight angle (about 15 degrees) so gravity pulls the bead of paint downward. Load your brush fully for each stroke, overlap slightly with the previous stroke, and work steadily without going back into drying areas. Pre-wet the paper for the smoothest results.

ArtCalcs

Wash Volume Calculator \u2014 Watercolour Mix Amounts

Calculate paint-to-water ratio and volume for large watercolour washes.

Wash Width

Width of the area to wash

Wash Height

Height of the area to wash

Wash TypeType of watercolour wash

Paint StrengthHow strong or diluted the wash

Number of Coats

How many layers of wash

Paper Weight

Weight of your watercolour paper

How We Calculate This

This calculator estimates the volume of diluted watercolour needed for washes based on the area to cover, paper absorbency and desired paint strength.

Volume formula

Base water = (Area ÷ 100) × 1.5ml × Absorbency factor

Total water = Base water × Coats × (1 + Buffer %)

Paint amount = Total water × (Strength ratio ÷ 100)

Strength ratios

Very light: 0.5% paint (1:200)
Light: 1% paint (1:100)
Medium: 3% paint (1:33)
Strong: 6% paint (1:17)

Frequently Asked Questions

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Calculate masking fluid needed for watercolour painting based on area to mask, coverage percentage and number of coats applied.

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Last updated: March 2026

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