The formula
cost/kg = Σ(phr × ₹/kg) ÷ Σ phr with loss = cost/kg ÷ (1 − loss%)
phr means parts per hundred rubber: every ingredient is stated against 100 parts of polymer. Because phr is a weight ratio, the weighted average of the prices IS the cost of one kg of the mix.
Worked example (prices illustrative)
- Natural rubber 100 phr × ₹180 = 18,000
- Carbon black N330 50 phr × ₹110 = 5,500
- Process oil 5 × ₹90 = 450 · Zinc oxide 5 × ₹250 = 1,250
- Stearic acid 1 × ₹120 = 120 · Sulphur 2.5 × ₹40 = 100 · Accelerator 1 × ₹400 = 400
- Total 164.5 phr, ₹25,820 → ₹156.96 per kg
- With 1.5% mixing loss: 156.96 ÷ 0.985 = ₹159.35 per kg
The part spreadsheets get wrong
The recipe is only half of it. When carbon black goes up tomorrow, every product made from this compound costs more - and in a spreadsheet nobody updates them all. In Aakar One the recipe publishes as a material with its own rate, so one republish reprices every product that uses it.
Questions people also ask
What does phr mean?
Parts per hundred rubber: the weight of each ingredient for every 100 parts of polymer by weight.
Should mixing loss be included in compound cost?
Yes. The material lost in the mill or mixer was paid for, so the good compound must carry it. Divide by (1 − loss) rather than adding the percentage, which slightly understates it.
Stop calculating this by hand
Aakar One does this arithmetic for every product and every size, then carries the result into the quote, the job card, stock and GST. Manufacturing ERP with CAD built in, made in India.