Volume and Liquidity — Avoiding the "Can't Sell When You Want To" Trap¶
For / Key Points
For: Investors who have traded stocks but never paid much attention to volume. Anyone unsure what "thin order book" means in practice.
Key Points:
- Volume measures how actively participants agree — the same price move means very different things at high volume versus low volume
- In thinly traded stocks, your own order moves the price against you, creating a hidden cost called slippage
- Checking average daily volume, spread, and book depth before trading is a precondition that comes before any valuation analysis
You want to buy 100,000 yen worth of stock. Stock A trades a million shares a day. Stock B trades 500 shares a day. Same P/E, same sector.
Are these the same risk? No. Stock B carries a risk that shows up on no chart and no valuation screen.
In the previous article, we described volume as the "weight of consensus." This time we go one step further and examine liquidity — whether you can actually sell when you want to sell, and buy when you want to buy.
Volume, Revisited¶
Volume is the total number of shares traded over a given period. If daily volume is one million shares, that many shares changed hands through agreements between buyers and sellers that day.
In the price-formation article, we used volume to gauge the reliability of price moves. A +3% rise on a million shares is more credible than the same rise on ten thousand shares, because more participants agreed on the direction.
That was one lens. Here is another: volume also tells you how easily a stock can be bought or sold. In finance, this ease of transacting is called liquidity.
What Liquidity Means — Can You Get Your Money Back?¶
Think about a savings account. Walk up to an ATM, withdraw any amount you like, and you get face value minus a small fee. That is extremely high liquidity.
Now think about real estate. Selling an apartment can take months. If you need to sell fast, you accept a price below market. That is low liquidity.
Stocks sit between these extremes. While the exchange is open, trades execute in seconds. But not every stock trades with the same ease. This is the point most beginners miss.
Large-cap stocks like Toyota or Apple trade tens of millions of shares daily. Selling 100,000 yen worth barely moves the price. But try the same with a micro-cap that trades a few hundred shares a day, and the situation is entirely different.
What Happens When the Order Book Is Thin¶
In the price-formation article, we examined the order book — the screen showing bid and ask orders. Liquidity problems play out right there.
A liquid stock's order book:
Ask side Bid side
1,503 50,000 shares
1,502 30,000 shares
1,501 20,000 shares
← ¥1 →
1,500 25,000 shares
1,499 35,000 shares
1,498 40,000 shares
The spread (gap between ask and bid) is ¥1. Tens of thousands of shares sit at each price level. A market buy order for 1,000 shares fills entirely at ¥1,501. The price barely moves.
An illiquid stock's order book:
Ask side Bid side
1,550 100 shares
1,520 50 shares
1,510 30 shares
← ¥15 →
1,495 20 shares
1,480 50 shares
1,450 30 shares
The spread is ¥15. Only dozens of shares sit at each level. A market buy for 1,000 shares eats through 30 shares at ¥1,510, then 50 at ¥1,520, then 100 at ¥1,550 — and you still need 820 more. The ask side runs dry, and you either wait or fill at much higher prices.
Your own order pushes the price against you. That is liquidity risk. It works the same way on the sell side: a rush to exit pushes the price down, and you end up selling far below the quote you saw when you decided to sell.
Slippage — The Gap Between Expected and Actual Price¶
The difference between the price when you place an order and the price at which it actually fills is called slippage.
In liquid stocks, slippage is nearly zero. In illiquid stocks, slippage becomes a real trading cost.
| High liquidity | Low liquidity | |
|---|---|---|
| Spread | Narrow (¥1–few yen) | Wide (¥10s or more) |
| Book depth | Heavy at each level | Sparse |
| Slippage | Near zero | Significant |
| Can you sell when you want? | Almost certainly | Uncertain |
Slippage does not appear on any brokerage fee schedule. It is a hidden cost. If your commission is ¥100 but slippage costs you ¥500, your true transaction cost is ¥600.
Beginners should especially note that slippage on exits is more dangerous than on entries. When buying, you can calmly decide whether the higher price is still acceptable. When selling — particularly during a stop-loss or panic — you tend to hit market sell. In an illiquid stock, that magnifies your loss by the slippage amount.
Sudden Volume Changes — Something Is Happening¶
Volume is not constant. Reading it requires distinguishing normal from abnormal.
Volume spikes. A stock that normally trades 50,000 shares a day suddenly trades a million. This means participants who previously ignored the stock have flooded in. The cause could be an earnings release, an M&A rumor, or sector-wide news, but the common thread is a signal that something is happening.
A volume spike paired with rising prices means broad buying consensus. Paired with falling prices, it means strong selling consensus. Either way, a volume spike validates that the current price move is not random noise.
Volume drying up. The opposite — a normally active stock goes quiet. Outside holiday periods, this signals fading interest. Price moves on low volume are less reliable; small trades can swing the price disproportionately.
Volume–price divergence. Prices rising while volume steadily declines is called divergence. It suggests the buying consensus is thinning and can foreshadow a reversal. Conversely, prices falling on rising volume signals genuine selling pressure.
How to Check Liquidity Before You Trade¶
Build a habit of checking liquidity before every trade. Three checkpoints:
Average daily volume. Look at the 20-day average (roughly one calendar month of trading days). A rule of thumb: the number of shares you want to trade should be less than 1% of average daily volume. If you want to buy 1,000 shares, look for stocks averaging at least 100,000 shares a day.
Spread. During trading hours, check the gap between the best bid and best ask. A spread within 0.1% of the stock price suggests ample liquidity. Above 0.5%, proceed with caution.
Book depth. Look beyond the best bid/ask and check 5–10 price levels in each direction. If sizable orders sit at each level, your order is unlikely to move the price much. If the book is sparse, your order may cause significant slippage.
These three checks alone prevent the majority of "bought but can't sell" situations.
Summary¶
- Volume measures both "conviction behind a price move" and "ease of trading" (liquidity)
- In illiquid stocks, your own order moves the price against you (slippage)
- Slippage is a hidden cost that appears on no fee schedule
- Sudden volume changes are signals — read them in combination with price direction
- Before trading, check average daily volume, spread, and book depth
P/E and P/B ratios assume you can exit a position whenever you want. When that assumption breaks down, no amount of attractive valuation saves you from being stuck. Liquidity is not a nice-to-have — it is a precondition for every other investment decision.