On Polymarket, volume is the dollar value of shares traded over a period; open interest is the value of shares still outstanding, money that stays at stake until the market resolves. On Nimb, volume sizes the circles on the map and the panel shows Polymarket's own 24H, 7D and 30D totals.
What are volume, liquidity and open interest?
- Volume
- Volume is the dollar value of shares that changed hands in a market over a period.
- Open interest
- Open interest is the value of shares that are still held and will pay out at resolution.
- Liquidity
- Liquidity is the money resting in the order book, ready to trade, at or near the current price.
- Informative volume
- Informative volume is money traded on outcomes that are still undecided, weighted by how far the price is from 0% or 100%, so trading on near-certain outcomes counts for less.
A simple way to keep them apart: volume is a flow (what happened), open interest is a stock (what is still exposed), liquidity is an offer (what could happen next). Telling them apart is a basic step in market reading.
Volume, liquidity, open interest: how do they compare?
| Metric | Measures | Changes when | Nimb uses it for |
|---|---|---|---|
| Volume | Dollars traded over the timeframe | Any trade happens, in either direction | Circle size on the map; panel rows "Volume · 7D" and "Volume · 30D"; market selection |
| Informative volume | Volume × how undecided the price is | Trades happen on outcomes priced away from 0% and 100% | The selection score that chooses which markets reach the map |
| Liquidity | Dollars resting in the order book | Orders are placed, filled or cancelled | "Liquidity in the book" row; the thin-book check in "Before you trade"; a selection gate |
| Open interest | Value of shares still outstanding | New shares are created or redeemed, not when existing ones change hands | Not shown in the panel |
A worked example. Ana buys 1,000 Yes shares at 41 cents while Ben buys 1,000 No shares at 59 cents. Polymarket matches the two orders and creates 1,000 new Yes/No pairs, each worth $1 at resolution. Next day Ana sells her 1,000 Yes shares to Cara at 45 cents: the same shares change owner, so volume rises and open interest does not. On day 3, Cara buys Ben's 1,000 No shares at 55 cents, holds full pairs and merges them back into $1,000, which removes them.
| Event | Volume added | Open interest after |
|---|---|---|
| Day 1: Ana buys Yes, Ben buys No, new pairs created | $410 on the Yes side | 1,000 pairs |
| Day 2: Ana sells Yes to Cara | $450 | 1,000 pairs |
| Day 3: Cara buys Ben's No and merges the pairs | $550 | 0 pairs |
Is high volume a good sign?
In market reading, volume answers one question: how tested is this price? High volume means many dollars have tested the price, so a single order is less likely to have set it. It does not mean the price is right, and it does not tell you direction. Three things to check before you read volume as strength:
- Where the money trades. $1M traded on an outcome at 97% says little: the question is nearly settled, and much of that trading is people collecting the last 3 cents.
- Who trades. Market makers trade both sides all day. Their volume adds liquidity, not opinion.
- When it traded. A 30D total can be one busy day three weeks ago. Compare 7D and 30D, and look at the money flow bars.
That is why Nimb's selection weights each outcome's volume by how undecided its price is:
I(p) = min(1, p(1 − p) / 0.16), and informative volume = Σ volume × I(p) over the event's outcomes.
| Price | I(p) | $1M of volume counts as |
|---|---|---|
| 20%–80% | 1.00 | $1,000,000 |
| 10% or 90% | 0.56 | $562,500 |
| 5% or 95% | 0.30 | $296,875 |
| 3% or 97% | 0.18 | $181,875 |
| 1% or 99% | 0.06 | $61,875 |
To reach the map, an event needs at least $5k (24H), $30k (7D) or $100k (30D) of informative volume. See market selection for the full score.
How does Nimb count volume, and why might it differ from Polymarket?
For 24H, 7D and 30D, the panel and the map use Polymarket's own volume totals from the Gamma API, refreshed every minute. These should match what Polymarket shows for the same outcome. For 1H, 12H and 3D, which Polymarket does not publish, Nimb estimates volume from recent trades.
The difference sits in the trade-level data. Nimb's own tests found that Polymarket's trades endpoint returns taker fills only by default. Counting those, Nimb's "$ traded" came to about 0.40× Polymarket's figure. Counting both maker and taker fills matched Polymarket within 1–3%. Nimb now shows Polymarket's maker+taker totals for volume, and keeps taker-only trades for one job: the direction of money flow.
Three reasons a figure can still differ:
- Outcome vs event. Polymarket's event page sums every outcome. Nimb's panel shows the outcome you selected; map circles sum the event's outcomes.
- Timing. Nimb refreshes volume every minute; a page you opened earlier can lag.
- Hidden outcomes. For events with many outcomes, Nimb loads detail for the most traded ones; see multi-outcome markets.
Why are circles bigger on 30D than on 24H?
On the map, a circle's area follows the money traded over the timeframe you chose, on a square-root scale. Thirty days of trading is more money than one day, so the same market carries more dollars on 30D. The map also re-sorts: a market that was busy three weeks ago but quiet today is large on 30D and may drop off 24H entirely. See timeframes for what each view is good for.
What can volume and open interest not tell you?
- Direction. Every trade has a buyer and a seller. Volume cannot say who was right or which side pushed; money flow approximates that.
- Accuracy. Heavily traded markets are often well calibrated, but not always. High volume around a rumour can still be wrong.
- Concentration. $500k of volume can be one wallet trading with itself through several addresses.
- Open interest. Nimb does not show open interest, so a holder figure such as "$400k held" cannot be read as a share of everything at stake in the market.
The other checks are in how to read a market; terms are in the glossary.
From reading to execution
When you read the market, volume tells you how tested a price is; liquidity tells you whether your order will fill near it. Check both, then size your order in the order ticket.
Last reviewed 2026-11-07 · Data from Polymarket · Not financial advice · Nimb is not affiliated with Polymarket.