Perlite Ratio Calculator for Potting Mixes

• Percentage mode: Ingredient volume = Total volume × (Ingredient % ÷ 100). Base medium % = 100 − (perlite + amendments).
• Parts mode: Ingredient volume = Total volume × (Ingredient parts ÷ Sum of parts).

1. Pick a method: percentages for quick planning, or parts for recipes.
2. Enter your total batch volume and choose a unit.
3. Set perlite and any amendments. Keep the total at 100%.
4. Add prices if you want a cost estimate for your batch.
5. Press Calculate and export results as CSV or PDF.

Perlite porosity and drainage targets

Perlite increases air space and speeds drainage in container media. Many growers target 25–35% perlite for general houseplants, 35–45% for seedlings, and 50–60% for cacti and succulents. The calculator lets you set a total batch volume, then converts your target percentage into a measurable volume in liters, gallons, quarts, or cubic feet.

Balancing moisture retention with structure

Adding compost or vermiculite raises water holding, while sand adds weight and stability. A practical starting blend is 30% perlite, 60% base medium, and 10% compost for mixed containers. If you increase perlite by 10 percentage points, consider reducing compost or vermiculite to keep the mix from drying too quickly. The base medium field auto-fills the remaining share.

Using parts to scale repeatable recipes

Parts mode is ideal when your recipe is written as “3:5:1” style ratios. Enter parts for each ingredient, and the tool computes both percentages and final volumes for your chosen batch size. This keeps recipes consistent when you move from a 10 L test batch to a 100 L production run, without redoing the math.

Estimating material costs per batch

Cost inputs are optional, but helpful for planning. Enter a price per selected unit for each ingredient, and the calculator multiplies unit price by the computed ingredient volume. This produces a single estimated batch cost, so you can compare recipes, suppliers, or bag sizes. Use the same unit for pricing and volume to avoid conversion errors.

Quality checks and exportable records

The tool prevents totals above 100% in percentage mode and flags impossible mixes. It also stores the last ten calculations in the session, making it easy to compare aeration targets across crops. Exporting to CSV supports spreadsheets and recordkeeping, while the PDF summary is useful for job sheets at the potting bench. For accuracy, measure ingredients loosely, then level the container. After moistening, the mix may settle 5 to 15%, so make a reserve batch for topping up.

FAQs

1) What perlite percentage works for most potted plants?

For many houseplants, 25–35% perlite supports drainage without drying too fast. Start near 30%, then adjust after a week of watering observations and root health.

2) Why does base medium change automatically?

In percentage mode, base medium is the remainder after perlite and amendments. This guarantees the mix totals 100%, preventing over-allocation that would inflate volumes and costs.

3) Should I measure by weight or volume?

This tool uses volume, which matches most gardening recipes. If you weigh materials, convert to volume using bulk density from your supplier, because perlite and compost densities vary widely.

4) How do I use parts mode correctly?

Enter any consistent ratio, such as 3 parts perlite and 5 parts base medium. The calculator divides each part by total parts to compute percentages and scaled volumes.

5) Can I include other ingredients not listed?

Yes. Use the closest category for planning, or treat the extra ingredient as part of base medium. Keep the totals realistic, then refine after observing drainage, compaction, and nutrient behavior.

6) Why might my final volume look slightly off in practice?

Dry components can settle when watered and packed, so real batch volume may shrink. Plan a 5–15% buffer for topping up pots, especially with very airy mixes.