Polar Games
Guide

How to Calculate a Percentage: Easy Formulas

What a percentage is, the three calculations you need most (X% of a number, what percent one number is of another, and discounts or increases), mental tricks and examples.

By Polarzinho ·

Official Riffvolt cover art

At the end of a Riffvolt round, the screen shows 93.95% accuracy. What does that mean? Out of every 100 notes, I hit about 94. A percentage is just that: a calculation "out of one hundred".

Here you get what a percentage is, the three formulas that solve almost every problem, mental tricks and examples with discounts, increases and tips.

Play Riffvolt

What is a percentage?

A percentage (percent, symbol %) is a fraction with a denominator of 100. Saying 25% means 25 out of every 100, or 25/100, which is the same as 1/4.

Fraction, decimal and percent

  • 1/2 = 0.5 = 50%
  • 1/4 = 0.25 = 25%
  • 3/4 = 0.75 = 75%
  • 1/5 = 0.2 = 20%
  • 1/10 = 0.1 = 10%

Formula 1: what is X% of a number

Multiply the number by X and divide by 100.

  • 20% of 150: 150 × 20 ÷ 100 = 30.
  • 10% of 340: 340 ÷ 10 = 34.
  • 25% of 120: 120 ÷ 4 = 30.

Formula 2: what percent one number is of another

Divide the part by the whole and multiply by 100.

  • 15 is what percent of 60? 15 ÷ 60 × 100 = 25%.
  • I hit 47 out of 50 notes: 47 ÷ 50 × 100 = 94%.

Formula 3: discounts, increases and tips

  • A 25% discount on something that costs $80: 80 × (1 − 0.25) = $60.
  • A 10% increase on 200: 200 × (1 + 0.10) = 220.
  • A 15% tip on a $20 meal: 20 × 15 ÷ 100 = $3.

Mental tricks

  • 10%: divide by 10.
  • 1%: divide by 100.
  • 50%: it is half.
  • 25%: it is half of half.
  • 20%: find 10% and double it.
  • 15%: find 10%, find half of that (5%) and add them.

Percentage points are not percent

If a game goes from 40% to 50% accuracy, it went up 10 percentage points. But compared with where it started, the increase is 25%, because 10 is 25% of 40.

Percentages in Riffvolt

In Riffvolt, a four-lane rhythm game, the results screen shows your grade and accuracy as a percentage. Accuracy is the share of notes you hit.

RIFFVOLT results screen with grade A, 93.95 percent accuracy, 106,755 points, max combo 193, a hits breakdown and a timing graph

Polarzinho93.95% is almost 94 out of 100. So close to a perfect grade.

Riffvolt: grade A, 93.95% accuracy and a max combo of 193.
OVERDRIVE banner with a bolt of lightning over the highway in Shake the Ceiling on Normal, combo 67 at x4
Riffvolt: overdrive kicks in when the ROCK meter fills.

FAQ

How do you calculate 10% of a number?

Divide the number by 10.

How do you calculate a discount?

Multiply the price by (1 − the discount as a decimal). With 25% off, multiply by 0.75.

What is 50% of 90?

45.

What is a percentage?

A fraction with a denominator of 100.

Your turn

What is 20% of 150? And 25% of 120? And 15 is what percent of 60? Answers: 30, 30 and 25%.

Play Riffvolt