⚖️ Proportional / Rule of Three Calculator
Know the Fair Price
for any Quantity
At the market, in the shop, at the counter — RateCalc instantly tells you the right price or quantity, so you're never confused or overcharged again.
800g = ₹350 → 305g = ₹134
1kg sugar = ₹40 → 500g = ₹20
1L milk = $2 → 750ml = $1.50
🏪
My Shop Items
Tap any item to load its price instantly
No items yet — tap + Add Item to save your products here.
🏪 Add New Item
Try a live example →
🍫 Chocolate🧂 Sugar🥛 Milk⛽ Fuel🧵 Fabric🍎 Fruit
1
Enter the Known Price & Quantity
The reference pair you already know — e.g. 800g costs ₹350
2
Enter New Price → Calculates Quantity
e.g. I have ₹134 — how much chocolate do I get?
Unknown Quantity
—
✓ RateCalc Answer
—
Cost per unit
—
Change
—
Ratio
—
📐 Formula Step-by-Step
—
Frequently Asked Questions
How do I find the price for a new quantity? ▾
Click Find Price tab. Enter known pair in Step 1, new quantity in Step 2. Formula: Unknown Price = (New Qty × Known Price) ÷ Known Qty.
How do I find the quantity for a new price? ▾
Keep Find Quantity tab. Enter known pair in Step 1, new price in Step 2. Formula: Unknown Qty = (New Price × Known Qty) ÷ Known Price.
Do I need to download an app? ▾
No. Works in any browser. Bookmark ratecalc.in for instant access at the market.
What units are supported? ▾
g, kg, ml, L, pcs, oz, lb, m, cm, ft. Auto-converts: 1500g shows as 1.5kg.
Which currencies are supported? ▾
₹ INR, $ USD, € EUR, £ GBP, AED, ¥ JPY, ৳ BDT, ₦ NGN, ₱ PHP, Kr SEK.