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Soil-block mix calculator

Scale your own measured batch to the number of blocks you need. Add a reserve, split your recipe by volume and see how many bags to buy.

How to measure a starting batch

1. Your measured yield

Measure the loose ingredients before adding water, then count the usable blocks they make. Use the same recipe, block size and technique for your next batch.

2. Your ingredient ratios

Use equal-volume parts from your own recipe. These blank rows do not recommend a mix. Bag sizes are optional; use the volume printed on each package.

Your batch plan

Enter your measured yield and recipe to calculate.

How to measure a useful starting batch

  1. Measure each loose ingredient with the same volume measure. Add their volumes together before adding water.
  2. Make blocks using your usual moisture level and pressure. Count only usable blocks.
  3. Enter that batch volume and count here. Scaling assumes your next batch uses the same ratios, block size and technique.

If you use a ready-made mix, enter it as one ingredient with 1 part. If you have no measured yield yet, make a small test batch first. We do not substitute an assumed compaction factor.

Method and worked example

Batch volume = target blocks ÷ measured blocks × measured batch volume. Reserve is added to that volume; each ingredient receives its share of the total parts. Whole bags round each ingredient up separately and assume you have none on hand.

For an illustrative yield of 40 blocks from 5 L, 100 blocks need 12.5 L before reserve, or 13.75 L with 10% extra. A 3:2:1 recipe splits that into 6.875 L, 4.5833 L and 2.2917 L. This is an arithmetic example, not a tested yield or recommended recipe.

Why not use block dimensions?

The volume of a finished cube is not the loose ingredient volume needed to make it. Water and compression change the relationship. Iowa State Extension’s soil-blocking guide explains mix and moisture considerations. This calculator does not recommend fertilizer, lime, watering or plant-health treatments.

Units and rounding

One cubic foot equals 28.316846592 L. Switching units preserves the entered physical volume. We avoid ambiguous dry versus liquid quarts and gallons; check your bag label. Displayed quantities use up to four decimal places; bag counts use unrounded values. Bag surplus is shown separately and is not added to the mixing recipe.

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