Bid-Ask Spread
Spread · Bid-offer spread · Bid-ask gap · Quote spread
The gap between the lowest ask and the highest bid in an order book: the least you lose by buying and then selling straight back.
Simple explanation
Background: Korean traders call it 스프레드 or 호가 차이 ("quote gap"). On Korean won markets each exchange's tick size puts a floor under it, and on low-priced coins that floor can be surprisingly wide.
An order book holds asks ("I'll sell at this price") and bids ("I'll buy at this price"). The lowest ask and the highest bid are the best quotes, and the distance between them is the spread. With the ask at ₩1,001 and the bid at ₩1,000, the spread is ₩1. To compare coins with very different prices, the spread is usually divided by the midpoint of the two quotes and shown as a percentage.
The spread is the price of trading right now. A market buy fills at the ask and a market sell at the bid, so if you buy and sell straight back you lose the spread even if the market has not moved at all. Fees come on top of that each way, and a large order adds slippage as it fills beyond the best quote. A maker who posts a limit order and waits trades at their own side of the book and does not pay the spread, but has no guarantee of being filled.
The spread exists because quoting is risky. Whoever leaves an order on the book does not know when it will fill, and the price may move against them in the meantime; the spread is their reward. Coins with heavy trading and thick books attract many competing quotes, so their spreads are tight; thinly traded or volatile coins have wide ones. Even for the same coin the spread can blow out in quiet hours such as the middle of the night, right after big news, right after a listing, or just after an exchange's maintenance ends. Within one exchange, the thinly traded BTC and USDT markets often have wider spreads than the won market.
The tick size, the smallest price step, is the floor of the spread: even quotes that touch are one tick apart. On Upbit's won market, coins at ₩1,000,000 (about $700) or more trade in ₩1,000 steps, so on a ₩100 million (about $71,400) bitcoin one step is only 0.001%; coins between ₩100 and ₩1,000 trade in ₩1 steps, so on a ₩120 coin one step is about 0.83%. The cheaper the coin, the more the tick size alone widens its spread in percentage terms. Tick sizes differ by exchange and do change; Upbit changed its won-market ticks several times in 2024 and 2025.
Price tables usually work out the kimchi premium from the last traded price. That price bounces inside the spread depending on whether the last fill hit the ask or the bid, so on a wide-spread coin the premium can flicker up and down with no real change in the market. And to capture a premium you would buy at the ask abroad and sell at the bid in Korea, so both spreads come out of the gap you see on screen.
"Spread" is also used loosely for any gap between two prices: the margin a bank adds to the market rate when you change money, the gap between futures and spot prices, the gap between two exchanges. Some people even call the kimchi premium "the Korea spread". Here it means the gap between the best bid and the best ask inside one exchange's order book, so whenever you see the word, check which two prices are being compared.
A wide spread is a cost you pay on every trade without seeing it on a bill. A limit order lets you avoid paying it outright but may not fill; a market order fills at once but accepts the spread and any slippage. Looking at how far apart the best bid and ask are, in percent, before you trade tells you roughly what that cost will be. Large orders on the book can also be cancelled at any moment before they fill, so a spread or depth you see now is no promise it will still be there.
CoinGaja's Kimchi Premium Calculator fills your amount through each exchange's live order book at the moment you calculate. Buying starts from the asks and selling from the bids, so both spreads and any slippage are included, and fees are taken off too, leaving what you would actually keep. On the price tables, a coin whose premium could shift by more than 1 percentage point from tick size alone has its premium hidden; that rule is published on the page explaining how CoinGaja calculates the premium.
Example
Bitcoin: bid ₩100,000,000 (about $71,400), ask ₩100,001,000 → spread ₩1,000 (about 0.001%)
Coin A: bid ₩120, ask ₩121 → spread ₩1 ÷ midpoint ₩120.5 = about 0.83%
Buy 10,000 Coin A at ₩121 and sell straight back at ₩120 → ₩1,210,000 − ₩1,200,000 = ₩10,000 (about $7) lost, before fees
With the overseas price at ₩119 in won → premium on the last price of ₩121 (the last fill was a buy) +1.68%; on the ₩120 bid you could actually sell at, +0.84%
At night the quotes widen to ₩118 bid and ₩124 ask → 6 ÷ 121 (the midpoint) = about 4.96%
※ Example numbers, for illustration only
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