Let-Down Ratio (LDR) & Addition Calculator
Convert between let-down ratio (1:X) and addition percentage, and split a finished blend into masterbatch and base resin. Updates as you type.
How the let-down ratio is defined
MatQuo uses one explicit convention: LDR 1:X means 1 part masterbatch in X parts of the total finished blend, so the masterbatch mass fraction is 1 / X and the percentage is 100 / X. Under this convention 1:20 = 5%, 1:25 = 4%, 1:50 = 2%.
Some suppliers quote the ratio against base resin instead (1 part MB per X parts resin), which is 1 / (X+1) of the blend. The result panel shows both conventions so you can confirm which your supplier means before dosing — the difference is small at low addition but grows as the rate rises.
The split
For a finished-blend quantity Q at mass fraction w: MB = Q × w, base resin = Q × (1 − w). Dosing is by mass; if your base resin and masterbatch have very different densities and you dose by volume, use the density-adjusted calculator.
Assumptions & limitations
Mass basis. No allowance for moisture, scrap/regrind, purge or line losses — add your own overage. This tool does not recommend an addition level; enter the rate specified by your masterbatch supplier or your own trials.
Method is shown in full here and computed by the shared MatQuo masterbatch engine (/tools/mb-engine.js); nothing is hidden in undisclosed constants.
FAQ
What does 1:X mean?
1 part masterbatch in X parts of total blend → MB fraction 1/X. 1:20 = 5%. The alternative "per X parts resin" convention (1/(X+1)) is also shown.
How do I convert % to a ratio?
X = 100 ÷ percentage (total-blend basis). 2% → 1:50.
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