Converting ppm to Percent

In fertilizer, compost, manure, and plant tissue samples both ppm and percent (%) data values are common. But how do they compare?

1% = 1 part/100 parts = 10,000 parts per 1,000,000 parts.

Both are units of concentration, just very different in magnitude. 10,000 ppm is the same as 1%. For larger concentrations % is commonly used to keep from reporting very large ppm numbers. With lower concentrations ppm is commonly used to avoid very small fractions of %. The reporting of nutrients in large ppm values is common on environmental reports for the analysis of biosolids.

The scale of the two units can be confusing. For example, a liquid fertilizer sample came to the lab for analysis and the results from total nitrogen was 0.14%. The customer called the lab concerned with such a small number. The customer had used test strips to do a rough estimation of the plant available nitrogen in the material. The material exceeded the maximum of test strips leading to a plant available nitrogen concentration of at least 500 ppm, how could the lab result be less than 1% total nitrogen? The 0.14% lab result was equal to 1,400 ppm total nitrogen.

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