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Copper Fungicide Dilution Calculator

Enter your water volume, dilution rate, and product copper content.

How it is calculated

The dilution rate is read as millilitres of product per litre of water. Product = Vwater × rate (mL). The finished spray volume is the water plus the product: Vtotal = Vwater × 1000 + product (mL), shown in litres. The copper concentration is (product × Cu% / 100) / Vtotal × 100, which treats one millilitre of product as carrying its percentage of copper per millilitre (a density of about 1). Results are rounded to 0.1 mL, 0.01 L and three decimals of a percent. All three inputs must be above zero. The copper % is whatever the label states (metallic copper equivalent or the compound), so use the same basis as the label's rate.

Worked example

You fill a 15 L sprayer, the label says 5 mL per litre, and the product contains 50% copper. Product needed: 15 × 5 = 75.0 mL. Total volume: 15 L = 15,000 mL plus 75 mL gives 15,075 mL, shown as 15.08 L. Copper in the product: 75 × 0.50 = 37.5. Concentration: 37.5 / 15,075 × 100 = 0.249%, the copper strength of the finished spray.

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Common mistakes

  • Entering a label rate given in grams per litre or ounces per gallon as if it were millilitres per litre; this tool expects mL per litre of water.
  • Entering the sprayer size in gallons. The water volume is in litres, so convert first (1 US gallon is about 3.785 L).
  • Confusing the copper content of the product (for example 50%) with the concentration of the finished spray (a fraction of a percent). The final figure is far smaller because the product is diluted in the water.
  • Using a rate meant for a different crop or disease stage. The calculator only does arithmetic, so the rate must come from the label for your crop.
  • Assuming a liquid and a powder behave alike. The maths treats the product as roughly 1 g per mL, so weigh powders rather than measuring them by volume if the label gives grams.

About this calculator

Copper-based fungicides (such as copper hydroxide, copper sulfate, or Bordeaux mixture) are diluted in water before spraying, and getting the dilution right matters because too little copper fails to control disease while too much can scorch foliage or build up to phytotoxic levels in the soil. This calculator takes your water volume, the product's labeled dilution rate, and its copper content percentage, and works out both how much product to add and the resulting elemental copper concentration of the finished spray.

Home gardeners, orchardists, and vineyard managers use copper sprays to control fungal and bacterial diseases like peach leaf curl, early blight, downy mildew, and fire blight, typically applying them preventively before wet weather. Because copper products vary widely in strength and are labeled in different units (ounces per gallon, grams per liter, or percentage metallic copper equivalent), this calculator helps translate the label instructions into an exact mixing amount for your sprayer.

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Comments (1)

  • Editorial team

    A quick sanity check on the third result: the finished spray holds only a small fraction of the product's copper percentage, because the product is spread through the whole tank. If the concentration comes out at several percent, the label rate was probably typed in grams per litre or ounces per gallon rather than millilitres per litre. Which crop and label rate are you working from?

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