15 times 17 is 255 — with the shortcut, the division facts and a drill to make it stick
15 × 17 = 255. That is the short answer, and it is the same answer whichever way round you write the two numbers. Below is where 255 comes from, the shortcut that gets you there without counting, the division facts that travel with it, and the fastest way to move it from "I can work it out" to "I just know it".
15 × 17 = 255. Said out loud in the way most classrooms say it: Fifteen seventeens are two hundred and fifty-five.
Multiplying is repeated addition, so 15 × 17 is fifteen seventeens added together, or equally seventeen fifteens added together. Both routes land on 255.
Written the other way round the answer does not change. 17 × 15 = 255 as well, because multiplication is commutative — the order of the two factors never affects the product. That halves how many facts you actually have to learn: get 15 × 17 and you have 17 × 15 for free.
Fifteen is ten plus half of ten. Ten seventeens are 170, half of that is 85, and 170 + 85 = 255.
Both factors are odd, so the answer has to be odd as well. 255 is odd, which rules out a whole class of slips.
Every multiplication fact comes with a division fact on its back. These four all say the same thing about 15, 17 and 255: 15 × 17 = 255; 17 × 15 = 255; 255 ÷ 15 = 17; 255 ÷ 17 = 15.
Learning them as one family rather than four separate things is the single biggest shortcut in times-table practice. If you can answer "255 divided by 15" as fast as you can answer "15 times 17", the fact is genuinely learned rather than just recognised.
In the 15 times table, 255 is the seventeenth step: 15, 30, 45, 60, 75, 90, 105, 120, 135, 150, 165, 180, 195, 210, 225, 240, 255.
In the 17 times table it is the fifteenth step instead: 17, 34, 51, 68, 85, 102, 119, 136, 153, 170, 187, 204, 221, 238, 255.
Seeing the same number arrive from two directions is what makes it stick. 255 is a landmark in both rows, so whichever table you are drilling you meet it again.
15 × 16 = 240, 15 × 18 = 270, 14 × 17 = 238, 16 × 17 = 272. Those are the answers people most often give by accident when they are a beat too quick.
The gap between neighbours is worth knowing on its own: each extra fifteen adds 15 to the running total, and each extra seventeen adds 17. So if 15 × 17 = 255 is solid, you can reach 15 × 18 by adding 15 rather than starting again.
Recognising a fact and recalling it under time pressure are different skills. A fact you can work out in four seconds still costs you four seconds every time it appears inside a longer calculation.
Short daily bursts beat long sessions: a 60-second drill every day will fix a table faster than one twenty-minute sitting a week. Mix the fact you are learning in among ones you already know so recall is being tested, not the order of a list.
15 times 17 is 255. In words, fifteen seventeens are two hundred and fifty-five.
17 times 15 is also 255. Swapping the two factors never changes the answer, so 17 × 15 and 15 × 17 both come to 255.
255 ÷ 15 = 17, because 15 × 17 = 255. The matching fact is 255 ÷ 17 = 15.
Fifteen is ten plus half of ten. Ten seventeens are 170, half of that is 85, and 170 + 85 = 255.
Yes. 255 is the seventeenth number in the 15 times table, and the fifteenth number in the 17 times table.
Every multiplication fact from 2 × 2 to 20 × 20 has its own page here, and the full grid is on the multiplication chart.