Long Multiplication: 21 × 8

"Long Multiplication Calculator" Calculator

Multiplicand (number to be multiplied)

Multiplier (number to multiply by)

What is 21 × 8?

Answer

21 × 8 = 168

21 × 8 and 8 × 21 are the same product — the order of the factors never changes the answer, only the working. Below, 21 is multiplied by 8 in a column, digit by digit.

21 × 8 in a Column

The multiplicand goes on top, the multiplier underneath, both aligned on the right. The multiplier has a single digit, so there is one partial product and the answer goes straight under the line.

  21
×  8
 168
21 × 8 = 168

Step-by-Step Solution

Step 1: Multiply the multiplicand by the last digit of the multiplier, 8: 21 × 8 = 168.

  • 1 × 8 = 8. Write 8.
  • 2 × 8 = 16. Write 6 and carry 1.
  • No digits are left, so the carried 1 is written in front: the partial product is 168.

21 × 8

=

168

Check It, and What It Is Not

Check by dividing back. Multiplication and division undo each other, so 168 ÷ 8 = 21 must come out exactly, with no remainder.

Fractions are a different calculation. Both factors here are whole numbers; for 2/3 or 2 3/4 use the fraction multiplication calculator, which multiplies numerators and denominators separately.

21 × 8 is a number, not an area. If those are the sides of a room in feet, the answer is 168 square feet — the same arithmetic, a different question, and it is answered by the square footage calculator.

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About "Long Multiplication Calculator" Calculator

This calculator multiplies two whole numbers the way it is done on paper: digit by digit, carrying where the column overflows, then adding the partial products together. For example, it can help you find out what is 21 × 8? (The answer is: 168). Enter the multiplicand (e.g. '21') and the multiplier (e.g. '8') and hit the button. The order of the two numbers does not matter — 21 × 8 and 8 × 21 are the same product — so either number can go on top. Fractions and mixed numbers belong to the fraction multiplication calculator, and the reverse operation is long division.

"Long Multiplication Calculator" Calculator

Multiplicand (number to be multiplied)

Multiplier (number to multiply by)

Products of 21

MultiplicationProduct
11 × 888
12 × 896
13 × 8104
14 × 8112
15 × 8120
16 × 8128
17 × 8136
18 × 8144
19 × 8152
20 × 8160
21 × 8168
22 × 8176
23 × 8184
24 × 8192
25 × 8200
26 × 8208
27 × 8216
28 × 8224
29 × 8232
30 × 8240

FAQ

What is 21 × 8?

21 × 8 = 168

Is 21 × 8 the same as 8 × 21?

Yes. Multiplication is commutative, so both come to 168. Only the working differs: this page multiplies by 8, which gives a single partial product.

How do you check that 21 × 8 = 168?

Divide the product back by one of the factors: 168 ÷ 8 = 21 exactly, with no remainder. Multiplication and division undo each other, which is what makes this check work.

What are the partial products of 21 × 8?

There is only one: the multiplier 8 has a single digit, so 21 × 8 = 168 is written straight under the line, with no addition step.

See Also