Formulation unit converter: wt%, vol%, PHR, solids and VOC
Enter a formulation once and see it as weight %, volume % and PHR, with weight solids, volume solids and VOC content in g/L on both the US (EPA) and EU/UK bases.
How the converter calculates each result
Every result comes from the formulation you enter: the amount of each component, its density, and its composition (solids, water and VOC as weight % of that component, from the SDS or supplier data). The tool first converts everything to grams and millilitres.
Weight % and volume %
Weight % is each component's share of the total mass. Volume % is each component's share of the total volume, where each volume is its mass divided by its density.
wt%(i) = 100 × m(i) / Σm
V(i) = m(i) / ρ(i); vol%(i) = 100 × V(i) / ΣV
The tool assumes volumes simply add when components are mixed. Real mixtures can shrink or expand by about 1–3%. If you enter a measured density for the mix, the VOC results use the measured volume instead.
PHR
PHR (parts per hundred rubber, or resin) gives each ingredient as a mass relative to 100 parts of the base polymer. If the base is a blend, the polymers together make up 100.
PHR(i) = 100 × m(i) / m(base); wt%(i) = 100 × PHR(i) / ΣPHR
Weight solids and volume solids
Weight solids is the non-volatile mass as a percentage of the total mass. Volume solids is the volume of the non-volatile part as a percentage of the calculated total volume.
Weight solids % = 100 × Σ(m(i) × solids%(i) / 100) / Σm
Volume solids % = 100 × ΣV(solids, i) / ΣV
For a component that is all solids or all volatile, the solids volume is simple. For an emulsion whose only volatile is water, the tool subtracts the volume of the water (at 0.997 g/mL). For other part-solid materials, such as a resin in solvent, it needs the solids density or the supplier's volume solids figure.
VOC content, US basis
The main US figure follows the federal formula in 40 CFR 59.406: grams of VOC per litre of coating, with water and exempt compounds removed from the volume. Enter the coating thinned to the manufacturer's maximum recommendation.
VOC, less water and exempt compounds (g/L) = 1000 × W(VOC) / (V − V(water) − V(exempt))
The tool also shows material VOC, which keeps water and exempt compounds in the volume. The federal architectural coatings rule (40 CFR 59 Subpart D) uses that basis only for low-solids stains and low-solids wood preservatives.
Material VOC (g/L) = 1000 × W(VOC) / V
VOC content, EU and UK basis
The EU/UK figure follows Directive 2004/42/EC and the UK's 2012 regulations, which use the same basis: grams of VOC per litre of ready-to-use product. Water is not removed from the volume. A VOC here is an organic compound with an initial boiling point of 250 °C or lower at 101.3 kPa.
VOC content, ready to use (g/L) = 1000 × W(VOC, EU) / V
Vehicle refinishing products use a different basis and are not covered.
What the tool does not do
These are calculated values, not measurements. For US compliance, EPA Method 24 results govern. In the EU and UK, the test methods in Annex III of the Directive apply. The tool does not classify chemicals: you decide which components count as VOC or as exempt.
Worked example: a water-borne acrylic paint
This is the example that loads when the page opens. The raw-material values are typical figures for illustration, not data from a specific supplier.
- Water: 224 g, 0.997 g/mL, 100% water
- Dispersant (ammonium polyacrylate, 40%): 8 g, 1.15 g/mL, 40% solids, 60% water
- Defoamer: 3 g, 0.87 g/mL, 100% solids
- Titanium dioxide (rutile): 220 g, 4.1 g/mL, 100% solids
- Calcium carbonate: 100 g, 2.71 g/mL, 100% solids
- Acrylic emulsion (50%): 400 g, 1.06 g/mL, 50% solids, 50% water
- Texanol coalescent: 20 g, 0.95 g/mL, a VOC under US rules but not under EU rules (boiling point about 254 °C)
- Propylene glycol: 10 g, 1.036 g/mL, a VOC under both
- HEUR thickener (20%): 15 g, 1.04 g/mL, 20% solids, 80% water
- Total mass is 1,000 g. Adding up each component's volume (mass ÷ density) gives 748.12 mL, so the calculated density is 1.3367 g/mL.
- Solids: 3.2 + 3 + 220 + 100 + 200 + 3 = 529.2 g, so weight solids is 52.92%. The solids take up 275.29 mL, so volume solids is 36.80%.
- Water: 224 + 4.8 + 200 + 12 = 440.8 g, which at 0.997 g/mL is 442.13 mL.
- US VOC: Texanol 20 g + propylene glycol 10 g = 30 g. Less water and exempt compounds: 1000 × 30 / (748.12 − 442.13) = 98.0 g/L (0.82 lb/gal). Material VOC: 1000 × 30 / 748.12 = 40.1 g/L.
- EU/UK VOC: only the propylene glycol counts, so 1000 × 10 / 748.12 = 13.4 g/L.
The same paint gives three quite different VOC figures. That is why the tool always states which basis each figure uses.
FAQs
Volume % compares the space each component takes up, and you can only get a volume from a mass by dividing by density. Without a density for every component the total volume is unknown, so the tool leaves volume % blank instead of guessing.
They differ in two ways. First, they count different compounds: in the US, almost every organic compound is a VOC unless it is on the EPA exempt list, while in the EU and UK a VOC is an organic compound with an initial boiling point of 250 °C or lower. Second, they use a different volume: the main US figure removes water and exempt compounds from the volume, while the EU/UK figure is per litre of ready-to-use product, water included. You cannot convert one figure into the other. Each has to be calculated from the formulation.
The US figure divides the VOC by the volume that is left after water and exempt compounds are removed. In a water-borne paint that volume is small, so the figure is high. This stops a product from looking lower in VOC just because it contains more water.
PHR means parts per hundred rubber (or resin). Each ingredient is given as a mass relative to 100 parts of the base polymer. For example, 50 phr of carbon black means 50 g of carbon black for every 100 g of rubber. If the base is a blend of polymers, they add up to 100 together.
It depends on which rules you report under. Acetone is on the US EPA list of exempt compounds, so it does not count as VOC in the US. Under the EU and UK definition it is a VOC, because its boiling point (about 56 °C) is below 250 °C.
It adds up the volume of the non-volatile part of each component and divides by the total volume. For pigments and other materials that are 100% solids, that is the whole component. For an emulsion whose only volatile is water, it subtracts the volume of the water. For other part-solid materials it needs the solids density or the supplier's volume solids figure, and it shows a dash if neither is given.
Use them as a formulation estimate, not as a test result. In the US, EPA Method 24 results govern where they differ from formulation data. In the EU and UK, the test methods in Annex III of Directive 2004/42/EC apply. Calculated values also miss effects such as volatiles released during curing.
No. The calculator runs entirely in your browser. Nothing you enter is sent to Uncountable or stored, and the CSV download is created on your own device.
References
- 40 CFR 59.406, Compliance provisions (VOC content equations), US Code of Federal Regulations www.law.cornell.edu
- 40 CFR 51.100(s), definition of volatile organic compounds and list of exempt compounds www.law.cornell.edu
- US EPA Method 24, volatile matter, water content, density, volume solids and weight solids of surface coatings (40 CFR Part 60, Appendix A-7)
- South Coast AQMD, VOC calculations www.aqmd.gov
- US EPA, Exclusion of exempt solvents from VOC calculations (1983 memo) www.epa.gov
- San Diego County APCD, How to calculate the VOC content of a mixed coating www.sdapcd.org
- Directive 2004/42/EC on VOC emissions from paints, varnishes and vehicle refinishing products eur-lex.europa.eu
- The Volatile Organic Compounds in Paints, Varnishes and Vehicle Refinishing Products Regulations 2012 (SI 2012/1715) www.legislation.gov.uk
- ISO 11890-1 and ISO 11890-2, Paints and varnishes: determination of volatile organic compound (VOC) content
- ASTM D5201, Standard Practice for Calculating Formulation Physical Constants of Paints and Coatings store.astm.org
- ASTM D1475 (density of liquid coatings) and ASTM D1566 (rubber terminology, including phr)
- NIST Special Publication 811, Guide for the Use of the International System of Units (conversion factors)
- Eastman, Texanol ester alcohol technical data (boiling point and EU VOC status)
Reviewed on 12 October, 2026. Formula sheet version 1.1.
Disclaimer
This converter is a free estimating tool. It calculates results from the values you enter and the assumptions shown on this page. The results are not measurements, and they are not legal, regulatory or professional advice.
The results do not replace testing with the official methods (EPA Method 24 in the US; the methods in Annex III of Directive 2004/42/EC in the EU and UK) or your own check of the rules that apply to your product and market. VOC rules and limits differ between countries, states and product categories, and they change. You are responsible for the values you enter, for how you classify each compound, and for any decision or regulatory submission you make.
We have taken care over the calculations, but the tool is provided as is. To the extent the law allows, Uncountable gives no warranty that the results are accurate, complete or suitable for any purpose, and accepts no liability for any loss that results from using them.
