Calculate unit conversion, percentages, and product unit prices by use case
Show the formula and units clearly, and check the unrounded value and the display for practical use separately.
Value and Unit to Convert
conversion result
After conversion, the value in each unit will be displayed.
The display is rounded for readability. The lower section shows the calculated value with more significant digits.
How to Calculate Ratio
Result
After calculation, the formula and the value before rounding will be displayed.
Items to Compare
Which Is Better Deal
Enter the price and quantity to calculate.
Check not only the unit price but also the amount you can use up, quality, expiration, shipping, and point conditions.
Input values are calculated only within your browser.
What you can do with the Unit, Percentage, and Better Deal Calculator
Convert units for length, weight, volume, speed, time, and area, and calculate what percentage, composition ratio, increase/decrease rate, discount, tax-included price, ratio allocation, and product unit price comparison on one screen.
We show the intermediate steps, comparison base, and unrounded values, so you can see which number was divided by what, rather than just the answer. All calculations are done in your browser, and no prices or input values are sent externally.
6 Categories of Unit Conversion
Convert mm, cm, m, km, inches, feet, mg, g, kg, ml, L, km/h, m/s, seconds, minutes, hours, days, and area.
Purpose-Based Input
Switch by input name for what percentage, composition ratio, increase/decrease rate, discount, tax, and ratio allocation.
Unit price including shipping and discounts
Compare the actual payment amount and base unit price including the displayed price, quantity, discount rate, and shipping.
Show Difference in Savings
Shows how much more expensive other products are in dollars and percentage compared to the lowest unit price.
How to Convert Units
- Choose type: length, weight, etc.Different types of units cannot be converted to each other, so first select the category.
- Enter value and unit to convert fromEnter the original values such as product display, speed, or work time as is.
- Select Target UnitCheck not only the result but also the full list of units in the same category.
- Check significant digits and useFor design, measurement, and contracts, separately check the required precision and rounding rules.
Main supported units
| Type | Units | Reference |
|---|---|---|
| Length | mm, cm, m, km, inch, ft, yard | 1 inch = 25.4 mm |
| Mass | mg, g, kg, t, oz, lb | 1 lb = 453.59237 g |
| Volume | ml, cc, dl, L, US cup, US fl oz | 1 US cup = 236.588 ml |
| Speed | m/s, km/h, mph, knot | 1 m/s = 3.6 km/h |
| Time | seconds, minutes, hours, days, weeks | 1 day = 24 hours |
| Area | mm², cm², m², ft², acre, ha, km² | 1 acre = 4046.8564224 m² |
Cup and fluid-ounce definitions vary by region. This English version uses US customary values; follow the product or recipe specification when precision matters.
Ratio & Change Rate Formulas
| What to Find | set | Example |
|---|---|---|
| B% of A | A × B ÷ 100 | 15% of 1,200 = 180 |
| A as % of B | A ÷ B × 100 | 30 is 25% of 120 |
| Change Rate from A to B | (B − A)÷ A × 100 | 100 to 120 is a 20% increase |
| after discount | Price × (1 − discount rate ÷ 100) | 20% off $2,000 = $1,600 |
| ratio split | Total × each ratio ÷ sum of ratios | 1,000 in a 2:3 ratio → 400 and 600 |
Order of discount and tax calculation
Usually, you apply discounts to the pre-tax price and then calculate consumption tax, but the amount you pay can differ based on store displays, coupons, points, and rounding rules. This tool calculates the discounted pre-tax equivalent, applies the tax rate, and then rounds as you specify.
In invoices, billing, and accounting, where you round—per item, per tax rate, or for the whole invoice—matters. For official tax calculations, use the invoice and consumption tax rounding tool and follow your business’s rules.
How to compare which is a better deal by unit price
- Select Same CategoryDo not mix weight, volume, and count; align them to a comparable quantity.
- Enter price and quantityMatch tax inclusion, item count, set size, and concentration ratio under the same conditions.
- Add discount and shippingGet closer to the amount you actually pay at purchase.
- Compare per 100g, 100ml, etc.Check the lowest unit price and the difference in amount and percentage from other products.
- Check if you can use it upMake the final decision including waste, storage space, expiration, and quality.
Rounding and precision of results
On-screen results are rounded to readable digits, but internal calculations use JavaScript’s double-precision floating point. For money, surveying, medical, or scientific calculations that require exact decimals or legally mandated rounding, recalculate in a dedicated system that follows the rules for that field.
We do not perform division by zero, negative quantities, or conversions that require density like weight to volume. Treating 1 ml of water as always 1 g can be incorrect for other substances.
Calculations without sending input
Unit conversion, percentages, increase/decrease rates, discounts, tax, ratios, unit prices, and comparison results are calculated in your browser. Prices, quantities, and product names are not sent to or saved on any server or external API. Reloading the page clears inputs and results.
Frequently asked questions about unit, percentage, and unit price calculations
Is 1 ml always 1 g?
No. Converting between weight and volume requires the density of the substance.
How many ml in a cup?
This English version uses a US cup: approximately 236.588 ml.
How to display when the increase rate is negative
Display as a decrease along with the absolute value.
Is the tax after discount accurate?
This is the result of the specified simple calculation order. Check the rounding rules for invoices separately.
Is the lowest unit price always the best deal?
No. Make a decision including quality, expiration, waste, shipping conditions, points, etc.
Are entered prices saved?
No saving or sending. Calculated in your browser.