20 times 20 is 400 — with the shortcut, the division facts and a drill to make it stick
20 × 20 = 400. Anything times twenty is doubling plus a zero, and this square is the landmark for every awkward fact in the high teens and low twenties.
20 × 20 = 400. Said out loud in the way most classrooms say it: Twenty twenties are four hundred.
Multiplying is repeated addition, so 20 × 20 is twenty twenties added together, or equally twenty twenties added together. Both routes land on 400.
Anything times 20 is "double it, then times ten": 2 × 20 = 40, so 20 × 20 = 400. It is the same fact as 2 × 2 = 4 with two zeros carried along, which is why it feels easy once seen.
Its real value is as an anchor for the awkward facts around it. 19 × 21 = 399 and 18 × 22 = 396, because two numbers the same distance either side of 20 multiply to 400 minus that distance squared. 21 × 21 = 400 + 20 + 20 + 1 = 441 and 19 × 19 = 400 − 20 − 20 + 1 = 361.
In the real world, 20 × 20 is a common garden and room measurement: a 20 ft by 20 ft space is 400 square feet, a common size for a two-car garage.
Method 1, times 2, then times ten: 20 is 2 × 10, so work out 20 × 2 = 40, then multiply by ten: 40 × 10 = 400.
Method 2, square the tens: 2 × 2 = 4, and each factor carries a zero, so add two zeros: 400.
Twenty is double ten. Double 20 to get 40, then write a zero on the end: 400.
20 × 20 is a square number: 400 is what you get when 20 is multiplied by itself, which is why the square root of 400 is 20.
Because one of the factors is even, the answer has to be even. 400 is, so the parity check passes.
20 × 20 = 400 and 400 ÷ 20 = 20 are one fact read in different directions. The facts either side — 20 × 19 = 380, 20 × 21 = 420, 19 × 20 = 380, 21 × 20 = 420 — are the answers people most often give by mistake when rushing, and each is just one twenty away from 400.
20 × 20 sits in two lists at once: row 20 of the twenty times table, and the twentieth square number. The highlighted row is 400.
| × | 20 times table | Square numbers |
|---|---|---|
| 1 | 20 × 1 = 20 | 1 × 1 = 1 |
| 2 | 20 × 2 = 40 | 2 × 2 = 4 |
| 3 | 20 × 3 = 60 | 3 × 3 = 9 |
| 4 | 20 × 4 = 80 | 4 × 4 = 16 |
| 5 | 20 × 5 = 100 | 5 × 5 = 25 |
| 6 | 20 × 6 = 120 | 6 × 6 = 36 |
| 7 | 20 × 7 = 140 | 7 × 7 = 49 |
| 8 | 20 × 8 = 160 | 8 × 8 = 64 |
| 9 | 20 × 9 = 180 | 9 × 9 = 81 |
| 10 | 20 × 10 = 200 | 10 × 10 = 100 |
| 11 | 20 × 11 = 220 | 11 × 11 = 121 |
| 12 | 20 × 12 = 240 | 12 × 12 = 144 |
| 13 | 20 × 13 = 260 | 13 × 13 = 169 |
| 14 | 20 × 14 = 280 | 14 × 14 = 196 |
| 15 | 20 × 15 = 300 | 15 × 15 = 225 |
| 16 | 20 × 16 = 320 | 16 × 16 = 256 |
| 17 | 20 × 17 = 340 | 17 × 17 = 289 |
| 18 | 20 × 18 = 360 | 18 × 18 = 324 |
| 19 | 20 × 19 = 380 | 19 × 19 = 361 |
| 20 | 20 × 20 = 400 | 20 × 20 = 400 |
These are the facts one step away from 20 × 20 in the grid, and the answers people give by mistake when rushing. The last column shows how far each lands from 400; tap a fact to open it or its times table.
| Fact | Answer | Compared with 400 |
|---|---|---|
| 20 × 19 | 380 | 20 less |
| 20 × 21 | 420 | 20 more |
| 19 × 20 | 380 | 20 less |
| 21 × 20 | 420 | 20 more |
| 19 × 21 | 399 | 1 less |
| 21 × 19 | 399 | 1 less |
Use the drill on this page for a 60-second quiz on 20 × 20 and its neighbours, read the 20 times table in full, or play the arcade game until the answer comes without counting.
20 times 20 is 400. In words, twenty twenties are four hundred.
400 ÷ 20 = 20, because 20 × 20 = 400.
Method 1, times 2, then times ten: 20 is 2 × 10, so work out 20 × 2 = 40, then multiply by ten: 40 × 10 = 400. Method 2, square the tens: 2 × 2 = 4, and each factor carries a zero, so add two zeros: 400.
Twenty times twenty is four hundred. Written as figures, 20 × 20 = 400.
Every times table from 1 to 20 is written out on the times tables page, with a drill for any row, and the full grid is on the multiplication chart.